Apple's official instructions are here:
https://support.apple.com/guide/font-book/restore-fonts-that-came-with-your-mac-fb34862/mac
"In the Font Book app on your Mac, choose Font Book > Settings.
Click Advanced, then click Reset Fonts.
Click Proceed to confirm, and enter your password if asked (or use Touch ID).
Any fonts you’ve installed are placed in /Library/Fonts (Removed) or in ~/Library/Fonts (Removed). To install those fonts again, just reinstall them."