Speak to Nebora that will reveal to be able to remove the collar but also that don't consider you worth of the service › article › divinity-original-sinhow-to-remove. After your conversation, Nebora will remove the Source Collar from your personal character.
Speak to Nebora, and confirm that you're the Fort Joy arena champion. Once you're outside again, pass through the Camp Kitchen and locate Nebora's tent down the steps just beyond the Shrine.