There are several ways you can address this:

1. By updating the variable stencilsheetstoken. After the user saves one field, their row number in the document is saved in this variable. So, if you were to say something like "Your user ID is X, use it the next time you return." and ask for the user ID when they enter the lesson and update stencilsheetstoken, that would put them back on the same row. Of course, it's not guaranteed that they will remember their ID and/or enter them correctly.

2. By using formulas. If each person has a unique identifier such as an email address, for example, you can first use SheetsSet to write a formula that would search the sheet for this email address. Then, right after SheetsSet, use SheetsGet to read the calculated result. If it returns a row number - save it to stencilsheetstoken, if there's no row number, then it's a new user, do nothing,

3. Again, save the unique identifier, such as an email and then later run a script in Google Sheets directly to merge rows with the same email.

Here's a blog post on using Google Sheets to authenticate users, you might find it helpful: https://cluelabs.com/blog/authenticating-a-user-in-articulate-storyline-with-the-help-of-the-google-sheets-widget/