set homeworld

hello

I want to know how can i set a new homeworld when I already did it once during the game.

Do I need to wait a lil time before do it again ? if yeah how long ?

Or once i did it i cant change it again?

I would like to set homeworld to the original planet.

I know that homeworld button is in details of the planet but I can't click on it ( grey button ).

Can you help me or explain me how to do that.

thx u very much