Does this phrase translate to "you could tell me if

Does this phrase translate to “you could tell me if he wanted.” The context makes it seem as if it is “you could tell me if you wanted” but this verb form appears to only work for first and third person, so that seems wrong as well.

If you want to use the second person, “you”, the correct form of the verb in Spanish is: quisieras.

What is the context?
“Quisiera” is the form for the first person singular of the Subjuntivo imperfecto and also the form for the third person singular. The third person singular is also used speaking to persons you address with “Usted”.

Thanks, that’s what I thought, the context is in one of the lessons. One of the interlocutors is trying to get someone to tell her about her brother and she replies, “you know something, but he won’t tell me.” It seemed more logical that she is saying, “you know something but you won’t tell me. The sentence reads: " Estoy segura de que usted sabe, pero no quiere decrime” so it looks like you’ve steered me right, she is saying that the guy she is talking about probably knows the thing her brother won’t tell her.

It is always better to mention the lesson you have a problem with: then people who want to help you can check the context,
In the Spanish sentence I don’t see any “quisiera”, I see “quiere”. - “I am sure that you know, but you don’t want to tell me”

Sorry it is the last sentence of the lesson “Lingq beginner - who is she?” lesson 3 and I put the wrong sentence in before… “pero usted podria decrime si quisiera” The final sentence of the lesson. Sorry this is my first request and I just started, excuse my botching it

No problem!
Pero usted podria decirme si usted quisiera: but you could tell me if you wanted. (= but you don’t want to tell me).