Yeah I would just practice with him rolling back onto his back in the daytime so you’re confident he is good with that, I know lots of babies sleep on their side or front, I try to think like we wouldn’t be comfy in one position all night so some babies won’t either :)
If they put themselves there then it's fine to leave them there x
Once they start doing it themselves there’s not much you can do about it. If they’re not happy they’ll roll themselves back. My first slept on her side from night 1, and was on her front by 12 weeks 🤦🏼♀️😂