Relax and lube!
Be the pitcher, not the catcher.
Get your partner to use their tongue
You can slowly train them but still use lube and it can be a wonderful experience.
The thing to do is to use lots and lots of lube, and go very very slowly. Possibly get some "practice" in advance with fingers or small butt plugs or ******. (Make sure anything you use has a flared ba<x>se so it can't "get lost" inside, necessitating an embarrassing trip to the emergency room to retrieve it.)
They sell a numbing cream ,use it the first few times and lube
No! Don't use numbing cream. VERY bad idea! Pain is a useful feedback mechanism, it means "slow down" or "stop" or "use more lube".
Lots of lube, go slow and take your time. Relax, don't tense up.
Relax... and enjoy it.