From DownSights: “Rebirth Island is a most notorious island, well known amongst the Call of Duty (COD) veterans, and makes its return as a separate map in Warzone. The new gameplay mechanics incorporated for this specific map go well with the name “Rebirth.”
Upon dying, you redeploy into the game, provided your teammates stay alive until the rebirth timer runs out. If they die before the timer runs out, you and your team will be out of the game for good. This mechanic helps in this easter egg as well. Given how small the Rebirth Island map is, you can expect to die a lot…A LOT.
You can also perform an easter egg on the island similar to how you’ve done the Bunker 11 and stadium easter eggs. There is a secret bunker on Rebirth Island which can be opened using a set number of codes acquired by performing a very tedious and lengthy easter egg.”
Source: N4G PC Rebirth Island Easter Egg Complete Comprehensive Guide