What to do after giving the fossil to the guy in Devon corp?

After giving the fossil to the researcher in Devon Corp in the Pokémon games, you will need to wait a period of time for the fossil to be regenerated into a Pokémon. This process typically takes a few in-game days. Once the fossil has been regenerated, you can return to the researcher to receive the resurrected Pokémon. Make sure you have an empty slot in your party to receive the Pokémon.