Welcome to the forum! I am a bit confused... if the bird gets on you, it is stepping up. Babies don't really require any training to step up, they WANT to get on us so all we need to do is put our hand in front of their chest and they will climb up (especially when they see the feeding syringe in our hand ). At 12 weeks old, you have a VERY young baby in your hands so it is possible that it's hard for it to step up with any type of grace, yet. A 12 week old baby would not have left the nest in the wild so it does not yet need a whole lot of balance or mobility... I know they look as if they were almost all grown but they are not, they are babies - and they will continue to be babies until they are six months old when they turn into juveniles.
What your bird needs now is handfeeding three times a day and two kinds of soft food served warm and fresh twice a day and lots and lots and lots of love and hours and hours and hours of one-on-one - just like a human baby would need.