Lock Pin Reset on Mac devices

Quit LumaShare completely

Open Terminal (Applications → Utilities → Terminal)

Run this command to find the preferences file:
find ~/Library/Containers -name "com.dslrbooth.fotoshare.plist" 2>/dev/null

Copy the full path from the output

Delete the file:
rm "PASTE_THE_FULL_PATH_HERE"

Relaunch LumaShare

The lock PIN will be gone. You will need to reconfigure your app settings.