My Turtle Has Laid An Egg, What Am I Supposed To Do With The Egg ?

I am very new tog blurtit I have seven turtles soon to be 8 but one of my turtles has laid an egg and I don't know what to with it I have taken it out of the tank and sat it in sand grass and a little bit if dirt the turtles possible parents are 2 of my turtles might have produced the egg they have yellow lines and a dark green shell.