don't, DON'T try to force the back pack up at all, you will break that hinge.
The correct way to transform the backpack for battroid:
1. the little antenna on the rear hatch should befully recessed, it should not be sticking out at all.
2. the hatch should be depressed, it should no longer be flush with the back but pressed down past the two nubs on either side.
3. the the back pack gets flipped up but no further pressure should be applied to try and make it sit higher. The top of the backpack should be level with the top of the hatch.
4. the hook on the top of the hatch should now be flipped over to secure the top of the back pack.
If you leave the antenna out, you'll stress that joint and it will break.
if you force that backpack past being level with the hatch, you will force the joint and it will break.