To change the note or interval enharmonic name for a note on the fretboard, just select the note and in the Inspector you'll see drop-down options for Note and Interval, like this:

Just click on the drop-down and change to the desired enharmonic:

The Apply to fretboard option will make the chosen enharmonic be used for any other matching notes on the fretboard, so you don't have to make the same change for each of them.

For automatic note enharmonics, you can set the key signature on a fretboard, like this: