welcome to the site
and welcome to the world of hi-power frustration. you either need 3 hands or a padded vise... but the firing pin spring replacement is THE pita of the bhp..... all guns have ONE thing that makes ya curse, this is the hi-powers one thing. it actually is fairly easy with the padded vise AND a few repetitions.
i found a field service manual in pdf, reinstallation of the firing pin assembly is on page 4 , hope it helps