Take your time and really get to know him and get him to trust you. A ton of ground work will help and just riding through the rough days will get him to trust you more.
If you mean he’s nervous, you can give him calming supplements, but ask your vet if they’re safe. Good Luck! ☺️☺️☺️💙 and you shouldn’t give this calming thing all the time, I think 💜