This may help, however it takes time... several sessions if necessary, however if it gets you over the line into the land of the anally experienced all is good!
Find a partner you trust!!! I repeat, find a partner you can trust.
Anal Rule #1 for newbies... too much lube is almost enough!
You may want to start with doing rectal temps if you are very, very tight just to get used to having an friendly intruder in you bottom.
Work up to a well lubed finger rimming your anus, then as you get used to the finger being on the outside move on to gently sliding that finger inside... one knuckle at a time stopping to work that tiny love knot into a relaxed state at each pause.
Once the finger is all the way in, gently rotate & withdraw the finger as you become adjusted to things.
For maximum effect quickly withdraw the finger about half way followed by a slow advance all the way in... take the most friction & quickness withdrawing the finger then a slower & more deliberate push back into the rectum.
As you become adjusted to a finger thrusting in & out of your butt you can move on to dildos, carrots, or small butt plugs to help you to learn how to accept larger & larger implements of pleasure.
Once you have learned to relax and receive you can move onto your ultimate prize.
Have your trusted partner take you slowly so you can adjust to having a firm cock stretching out your freshly lubed & fingered love knot... filling your beautiful behind with pure pleasure!
Don't be afraid... jump in & enjoy. 😁