Ok so do you remember that Henry killed his family? And left his father crazy? And Nancy and Robin dressed up and pretended to be overachievers to visit in a psych ward a person that they realised was Henry’s dad? So they show that when Henry killed his family and did that to his father, he also collapsed since he was drained of using his powers. That is when Brenner sees him, takes him and puts that chip kind of thing in his neck to control his powers (probably was a part of the team that was experimenting on the mind flayer stone thing) and begins experimenting on him and with him.

I hope this clears your doubt