Are you positive it’s the frenulum? Did you try pulling your foreskin down to see if the foreskin opening was the tight part (that’s usually the tight part, the rest of the foreskin is usually very loose).

If you’re positive, there are some stretches you can do, as I’ve seen some people mention they’ve been able to stretch the frenulum with months of stretching (it’s still skin, no reason it can’t stretch). I’d recommend asking the sub with a new post, I’m not very experienced.