Hello. I bought starboard foil and In my formula board I have DTB and the mast head not fit. Should I cut it?

Wow, I had a 60mm gap above the top of the deep tuttle mast head in my formula board.

I doubt it. Have you measured the box depth. You will probably need to make a spacer to fill the gap rather than cut. A bit of carefull sanding back and front edge may be required to let it go in deeper. If it only sticks out a few mm dont bother. If your box isnt foil ready defo make a spacer, using a mast without a flange or power plate set up it probably will break the box.

I have the opposite problem.

i think in your case, you're better off seeing if you can get an old mast with the correct head on it (as someone mentioned earlier)

it is surprising that you need to cut yours ;
i have the same mast and it fits my foil box perfectly after some very light sanding.
my foil box measures 68mm deep at the front screw and also 68mm deep at the back screw and it is the same box used by a few different board brands.
my other non-foil DT boxes are all deeper.