Hacking. That is one way.
Another way does not allow you to manipulate all of the IVs, just 2 really. You have 2 Pokemon:
Tar1 (Tyranitar) - 31 Atk
Tar2 (Tyranitar)- 31 HP
If you give Tar1 the Power Bracer to hold and give Tar2 the Power Weight, They will both pass down their perfect IVs for Atk & HP. The other IVs would be randomly chosen from the parents. If those other IVs are perfect or good, the baby has a pretty good set of IVs.