PM a host to get their attention and also immediately post this image in your confessionals to claim it.
You can use it up to and through the final 6. You can play it on yourself or someone else in the 5 minute window after Jeff leaves to tally the votes.
If you wish to give it away before Tribal Council, you must post in the designated thread in your confessionals saying so. After that point you relinquish all power over the idol and it is no longer in your possession.
Good luck!