What do the sources have to say about the following situation? A person helps to make a minyan for mincha at the earliest possible time on a long summer's day. He forgets that he did this and goes to synagogue for his regular mincha minyan. He is asked to lead the prayers and only after saying the quiet Amidah realises that he has already prayed.
Can he continue to repeat the Amidah on the grounds that this will be to fulfil the obligation of anyone in the community who does not know how to pray or should he stand down and get someone to replace him.
related: Said mincha twice: now what?