You're not alone thinking that

If you can set IN & OUT points, then the only other one you'll need is a TO point, and this is just the current time position. The IN & OUT points mark the start & end of a section of your track or song, and the TO point is where you want to move the section. So you'd locate your time position to just before the song starts, then set IN. Then locate to just after the end of the song and set OUT. Then rewind so the current time position is zero (this is now the TO point). Then you can use the reqd Track Edit function, e.g. Move/Paste. This will move the section defined by IN & OUT for the specified track or tracks or song, to the TO position, i.e. time zero.
To get rid of any rubbish at the end of the moved song, set the IN & OUT points to encompass the rubbish and use the Silence function.
N.B. I don't have a dp03 but the track edit functions are very similar to the dp32, which I do have. The actual method for setting IN/OUT & TO points may not be exactly as I've described, but their function is correct.
Update: Note you don't
need to move the song if you're going to mix it on the dp03. When you mix, you have to specify the IN & OUT points for the section to be mixed, and the machine will just process that section and create the result starting at time zero.