Constantly forgets things and doesn't speak very good english.

[AliceDee1992]

Need help on how to help him remember and to start speaking normal! Me and my partner are out of ideas.

Is English his only language?

Has anything happened which might create a regression? Can he hear properly or is he being silly and messing around to be funny?

How old is he OP?

How old is he? Is English his first language?

I'm sure you've been told, but the way to encourage language is turn round what they've said. Conversations go:

"Car"
"Yes, that's a red car."

or "I drinked it"
"That's right you Drank it"

I'm just going to pick up on something from your op. I don't usually pick up on grammar here.
You wrote "start speaking normal"
The correct English is "start speaking normally". It's probably just typing quickly, but it's easy to get lazy with speech and the children pick up on it. So if you have a child who's struggling with learning English, having parents model it correctly helps.