The CG of a helicopter is not as critical as on a plane.
Having said that, it does still have an influence.
Optimum CG is on the mainshaft or slightly forward. A slightly backwards CG does not have the dramatic effect as on a plane.
The usual cause for pitching up is too light a flybar, too light mainblades and CG of mainblades being too far back (chordwise).
Delta offset can also be the cause, but is usually not adjustable on small and cheaper helis.
To improve the situation:
Adjust CG to be on or slightly forward of mast
Increase weight of the flybar via flybar weights.
Purchase or move CG forward on the main blades

I don't know this specific model, but if it's delta offset in the head is specifically designed for beginners..ie stable, then I don't think that there is a lot that you can do about it.