Google Sheet Script - if statement

I know next to nothing about writing scripts in Google Sheets, but I'm hoping to learn!

I've gotten a cell to increase by 1 when I click a drawing, but I need for the cell to go back to 1 after it gets to 12. So it continually counts from 1 up to 12.

I have this as the original script. I know how to write and if statement as a formula, but not in a script. Can anyone help?

function incrementup() {
  SpreadsheetApp.getActiveSheet().getRange('T38').setValue(SpreadsheetApp.getActiveSheet().getRange('T38').getValue() + 1);
}

Thanks so much!