Question: What happens when a player calls a discard but, picks up the wrong tile and adds it to the exposure? Can he put the wrong tile back on the table and take the correct one?

Answer: It is every player’s responsibility to verify they’ve made a correct exposure. If a player calls a tile for exposure and picks up the wrong tile, they now have an invalid exposure and their hand should be declared dead. 

Source: Mah Jongg Made Easy 2024, page 19, #15(c)