Remove clasp from SD43 bracelet

[samson66]

I'm trying to remove the clasp from the bracelet on my SD43 to install a rubber b strap. Struggling already. I doubt this has ever been removed in the five years I've owned it.

Couple questions. What is the correct screw driver size if anyone knows? And what's the trick for breaking it loose? Use a hair dryer or something?

Wondering if this might be a job for a watchmaker, at least the first time anyway?

Any tips or help appreciated