Hey, I had this exact issue before I lost my virginity (although I don’t know if it was vaginismus, never had it checked out).

It’s important that your first time is with someone who’s patient and willing to work with you and what you need. A lot of emphasis on this, because you’re going to have to go super slow so it’s comfortable for you.

Get a bunch of lube, have a lot of foreplay beforehand (making out etc, that’ll help you relax), and go absolutely as slow as you need. It will most likely be painful! But in my experience, after the first time I never had major issues with penetration again (but this may be different for you).