How to stop AirPods(4th gen) from falling off the ear?

Have you tried the different sized tips that come with the AirPods, i.e. small, medium and large.

There are a number of alternate ear tips offered on Amazon.com like "UPDENI 6 Pairs Ear Cover for AirPods 4, Anti Slip Ear Skin Tips"

Also there are "hooks" for AirPods that hook over the ear. "ALXCD Ear Hooks Compatible with AirPods 4 4th Generation Earbuds, Adjustable Over-Ear Soft Earhook".

If they keep falling out of your ear i am afraid that the fit is not well for you the AirPods 4 cannot be used with different eartips so there is not a lot you can do i am afraid