For the time being, if there are two of you there, have one person offer him a treat and let him nibble on it (without letting the treat go) while the other clips his collar and leash on. I would also practice a sit/stay whereby you have him sit, show him the collar and leash, hide the collar and leash again, then release and reward him for staying in the sit. Repeat until you can gradually show him the collar and bring it closer to his face head before releasing and rewarding him. Keep repeating until you can get the collar all the way around his neck. If he jumps up, take the collar away, put him back in a sit and start again but only reach a partial distance towards him with the collar. Hope that makes sense.
To keep the process simple, make sure the leash is already attached to the collar before putting the collar on. If you have the type of collar that slips over his head, here’s how I would teach him to ‘get dressed’: https://www.youtube.com/watch?v=mg28CYIA6O4.