I’m currently following the OVT program, but I’ve found that a large problem I have is that my left arm is A LOT weaker than my right. This problem appears when i do all upper body exercises. I was wondering what would be the best way to make my left side as strong as my right.
do unilateral exercises only for a while.
start with your ‘weak’ side and perform only as many reps with your ‘stronger’ side as you’ve completed with your ‘weaker’ one, even if it doesn’t completely fatigue the muscle group
3 ways of sorting this as far as I can see.
1 - Do as Petrichor says
2 - Only train as heavy as the weak side will allow until it catches up.
3 - Use your other hand for your nocturnal experiments. 
I think of it this way. You’ve lived your whole life using your dominant arm/hand for all difficult tasks. That is, until you start to lift weights. There is no miracle cure that is going to make your left arm catch up in strength to your right arm in a matter of weeks. Give it time and it will balance itself out, just don’t show preference to your strong arm and isolate it with heavier lifts.
Use dumbells. If you fail on one side, stop.