It's been almost 30 years since I've done one, and I'm too lazy to partially disassemble one of mine - but - IIRC :
Step one is, remove the barrels from the frame
Two - remove the buttstock from the frame.
Three, cock the hammer & pin the mainspring strut to relieve spring tension on the hammer.
Four, remove the mainspring & drive out it's pivot pin to remove the hammer.
* * * * * * *
The side selector should now be accessable for switching out if a replacement in on hand.
Reassemble in reverse order.
(take 2 aspirin, call us in the morning
)
If the "replacement" selector is actually a new hammer with the selector in it's pivoting nose, simply reinstall the hammer/mainspring, using the new hammer after first removing/discarding the broken side selector parts. (they are irrepairable, believe me when I tell you this)
Re-install the buttstock, and cover the side button hole with a dime (epoxy), or whatever.
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