TinkerCAD basically works by generating objects and object-shaped holes that you can merge to create the final design. If you had designed the ocarina from scratch in TinkerCAD, you could move the object-shaped holes around before merging.

Since you’re importing the model, TinkerCAD treats it as one pre built shape. The best you can do is generate new objects to fill the holes, and generate new holes that you can put where you want. However, since this is a musical instrument, moving the holes can change the effect they have on pitch.

I found at least one ocarina model designed to be played with one hand, with appropriate hole placement. I’d recommend starting with that, rather than moving the holes yourself. Unless of course you know enough about ocarina design to keep the thing tuned properly, in which case just fill the holes and generate new ones.