The second I say something wrong is correct. No extra conjugation needed to refer to future. 'The second' refers to a specific point in time because of the use of 'tell me'.

First, “say something wrong” often has the sense of being insensitive or hurtful. It wouldn’t be a natural choice if you’re talking about language errors. As far as the tense, both are ok but “say” would would be better if the request is habitual. Also to be considered is “I’ve said”. “Saying” is slightly incompatible with “the second” because but certainly something you could hear. I’m making mistakes, aren’t I? Tell me when I do. Tell me the second I make a mistake. (In general) Tell me the second I’ve made a mistake. (The first one)

without changing your sentence at all the answer is: "tell me the second i say something wrong" it would sound better to say it like this: The second i say something wrong, tell me

I don't understand what did you mean " tell me the second". Can you explain more details? I guess you want to say " if I say something wrong, please correct my mistake"

I said something wrong. ( Past tense)