Ensure the door isn't in "Vacation" or "Lock" mode when it won't respond to the remote from the outside. When in one of these modes it may open once using the remote, then must be unlocked from the wall control inside the garage.
Start by cleaning the tracks with a rag to eliminate any build-up that might be interfering with your door’s gentle glide. Don’t lubricate the tracks, but ensuring they’re clean is essential to your door’s functioning.
Fix: Replace batteries or buy a new remote or receiver
If the wall switch works but one of the remotes doesn't, check the batteries first. Still nothing? — You may need a new remote. Home centers carry a few models, and you can find a wide selection online.