When you're starting out in the editor, you're first going to add at least one table. However, as you're working with your data in the editor, you may realize you need to make changes to your spreadsheet. You may decide to remove a column, add a column, or rearrange your columns. Then, you run into something like this in the emulator:
Here's how you resolve the problem.
Let's say this is your original spreadsheet; you have these three columns:
Then, you decide to add another column in your spreadsheet:
In the Data tab, go to the columns section and find the table for which you just made changes.
Then, select "regenerate":
Then, select "regenerate".
When you sync in the emulator, you'll now be able to see your additional column in whatever view(s) you have set up.
Remember to regenerate your columns whenever you make changes to the number or order of columns you have in a table.
Regenerating apps build from a Google Forms
If the app was built from a Google Form, the original form configuration will be stored in the response sheet in the form of notes attached to the header row. Regenerating will cause the columns to restore the settings contained within the notes, potentially overwriting changes you've made in the editor. To avoid this, remove the notes from the response sheet before regenerating. If you do accidentally regenerate with notes left in the sheet and lose your configuration, remember that you can restore an older version of the app using Version History.
You may not need to modify the sheet at all
If you just want to hide or reorder some columns within the app, there are several ways to do so without modifying the underlying sheet.