Does he follow instructions Lauren?
In the daytime, with things like take this to the kitchen, put that in the bin, bring the ball to me, put Peppa Pig on the sofa, sit down please, etc etc.
I would start working on following instructions with lots of instruction-following in the daytime with big praise when he follows the instruction.
Then at bedtime, stop lying him down. Stop completely. So put him in the cot standing up, tap the matreess and tell him to lie down. Wait expectantly for a few moments and repeat if needed. Praise when he does lie down himself and give him some close attention in the cot (leaning over, giving a kiss or cuddle if you can reach) and retreat to your normal position where you stay as he goes to sleep.
If he makes any move to stand up or sit up, be completely on the ball and ready to set your expectations - that he needs to lie down in order to go to sleep. So go to him immediately and without any faffing around give the instruction to lie down and tap the mattress.
This can only work though if you have spent some time playing instruction following games beforehand, with lots if praise. You need your child to want to do something when you ask him to, or it won't work.