i lost the mission buttons and i eant them back how do i get them back.

If you closed the missions, you can't get them back.

If you go and make a colony in another world, you can get the missions in that world and the resources that you get on completing missions will be added on that world.
Or you may wait till the current era ends and new era starts on the world you are playing on. Then you will get the missions back.

In short whenever you build a new colony, you will get the missions.

Now u can't get the missions back in that era