Grace notes in tablature

In the attached file, there are grace notes in most measures. In the tablature staff the default fret numbers for the grace notes were the ones desired. However, in measure 17 when I add the grace notes I want to override the default fret numbers, but could not figure out how to edit them. I have added the notes that I want to be grace notes as 16ths to show the desired fret numbers.

Is there a way to edit the fret numbers of grace notes, or alternatively, promote regular notes to grace notes?