The Insert Keys Task in Polus is a simple common task which means if 1 crewmate has it, everyone else should aswell. All you have to do is drag the key from the left to the highlighted keyhole, insert it and rotate the key 90 degrees to the left or right.
There is a trick to catch impostors faking this task. The keyhole's position is determined by the order in which players entered the lobby, for example the host will always have the first keyhole on the left. You can catch an impostor lying by asking them what keyhole they had, for example they are the third player to join, but they say they had the one on the top left.