Firebase: How do I update the same document that was created during a Gen 2 onDocumentCreated trigger event?

I can’t get my trigger to update the same document that is being created. I printed out debug statements to the console and the error points to documentData.set. I’ve tried document.ref.update, documentData.ref.set, and documentData.set, but none of these work. The console shows these errors below. How do I update the same document that is being created during the create trigger?

document.ref.update: 

TypeError: Cannot read properties of undefined (reading ‘update’)

documentData.ref.set:

TypeError: Cannot read properties of undefined (reading ‘set’)

documentData.set:

TypeError: documentData.set is not a function

exports.onFriendAdded = onDocumentCreated(
  "users/{userDocID}/friends/{friendDocID}",
  async (event: any) => {
    const timestamp = getTimestamp();
    const document = event;
    const documentData = document.data.data();
    const moveOnToNextStep = documentData.moveOnToNextStep;
    let friendUID = documentData.uid;

    if (!moveOnToNextStep) {
      return;
    }

    console.log(myAppTag + " onFriendAdded started!");

    // If the friend uid = empty/null, update it
    if (friendUID == "" || friendUID == null) {
      console.log(myAppTag + " 1");
      const friendUsername = documentData.username;
      const friendInfo = await getUserInfo(1, friendUsername, "uid");
      console.log(myAppTag + " 2");

      if (friendInfo[0] == 1) {
        friendUID = friendInfo[2];
        console.log(myAppTag + " 3");

        // If sendFriendRequest = true, send a notification to the friend Doing
        // this here because updating the friendUID causes the onUpdate to fire
        // and don't want to double send the request.
        const sendFriendRequest = documentData.sendFriendRequest;

        if (sendFriendRequest) {
          console.log(myAppTag + " 4");
          const uid = event.params.userDocID;
          let username = "";

          const friendStatus = await getFriendStatus(uid, friendUID);
          console.log(myAppTag + " 5");

          if (friendStatus["returnVal"] == 0) {
            console.log(myAppTag + " 6");
            // If friend stat cant be found, dont send friend request
            console.log(
              myAppTag +
                " onFriendUpdated getFriendStatus returnVal is 0. Error: " +
                friendStatus["returnMsg"]
            );
            documentData.ref.set({
              sendFriendRequest: false,
              modifiedDate: timestamp,
            });
            return;
          }

          if (friendStatus["status"] == "0") {
            console.log(myAppTag + " 7");
            console.log(
              myAppTag +
                `onFriendUpdated getFriendStatus user B has blocked user
                A. status: ` +
                friendStatus["status"]
            );
            documentData.ref.set({
              sendFriendRequest: false,
              modifiedDate: timestamp,
            });
            return;
          }

          const userInfo = await getUserInfo(0, uid, "username");
          console.log(myAppTag + " 8");

          if (userInfo[0] == 1) {
            username = userInfo[2];
          }

          if (username == "" || username == null) {
            console.log(
              myAppTag +
                " onFriendAdded Error when getting user info: " +
                userInfo[1]
            );
            return;
          }
          console.log(myAppTag + " 9");
          const notifResult = await sendNotification(
            uid,
            username,
            friendUID,
            friendUsername,
            notifIDFriendRequest
          );
          console.log(myAppTag + " 10");

          if (notifResult[0] == 1) {
            console.log(myAppTag + " 11");
            documentData.set({ // ERROR POINTS HERE 
              sendFriendRequest: false,
              modifiedDate: timestamp,
            });
            console.log(myAppTag + " 11.1");
          } else {
            console.log(myAppTag + " 12");
            console.error(
              myAppTag +
                " onFriendAdded Error when sending the notification." +
                " uid: " +
                uid +
                " username: " +
                username +
                " friendUID: " +
                friendUID +
                " friendUsername: " +
                friendUsername +
                " returnVal: " +
                notifResult[0] +
                " returnMsg: " +
                notifResult[1]
            );
          }
        }
        console.log(myAppTag + " 12.1");
        documentData.ref.set({
          // Update "document" with the new data
          uid: friendUID,
          modifiedDate: timestamp,
        });
        console.log(myAppTag + " 13");
      } else {
        console.log(
          myAppTag +
            " onFriendAdded Error when getting friend info: " +
            friendInfo[1]
        );
        return; // The friend request (below) will not be sent
      }
    }
    console.log(myAppTag + " 14");
    await documentData.ref.set({
      moveOnToNextStep: false,
      modifiedDate: timestamp,
    });
  }
);