Form: Auto-Fill a column based on previous enum selection

I would like to fill the next column on a table based on what was selected from an enum list on a form. Example: The user selects a school, I want to put the school’s reference ID in the next column. I have the table all set up for this, and I understand how to do conditional dropdowns using Valid If. Using Valid If, I can get it so the form shows the one value that I want to populate, but the user has to select it. I’d like it to just automatically happen when they make the first selection.

I hope that makes sense. Let me know if you’d like any screenshots other other specifics.

Edit: I am currently accomplishing this on the spreadsheet end using the Auto Compute -> Spreadsheet Formula functionality, but I would love to make it work within the app.