illegal Sub/CR

[Lastump]

When an illegal CR is sent into the game (illegal sub) is this an appeal only or not. If not at what point does the PU, call the illegal sub out? CR Jones runs for F2 in the 1st inning, in the 3rd inning CR smith (who already ran for F1) is sent out. Do i let it happen and before the next pitch call the illegal sub or is this an appeal.

(And yes i now preventive umpiring would not let the wrong CR come out in the first place but certainly if the coach can't keep track of which players are legal or not who am i to say otherwsie.)

thanks