Is there a past tense for "Ça y est" using "Ça y etais = That's it, It was done"

They're not pronounced quite the same. Ça y était = [sa je te] Ça a été = [sa a e te] On their own, the meaning is very similar - it was ok, it worked out. I'll ask Aurélie, who is a native speaker, to respond in detail.

Bonjour Paul !

Though you can technically conjugate this expression in past tenses, you will never really use it in other contexts than the present.
Indeed, "ça y est" expresses some kind of immediate relief after an action been completed, hence its strong link with the present.
You could possibly encounter "ça y était" in indirect speech, when reported someone's words, but none of the other forms would be used by a native (including the future).

I hope that's helpful!
Aurélie

"Ça a été" and "ça y était" are two different expressions, with different meanings and uses:

- Like I said above, "ça y était", means either literally "it/this was there" or, just like "ça y est", it can mean "here it was/it was done/I was done" in a context of indirect speech.

- "Ça a été" literally means "it's been/it was", and as a fixed expression is used to express "it's been ok/it was ok", like at the restaurant for example:
Serveur: Ça a été ? (It's been fine? / How was it?)
Client: Oui, très bien merci.

I hope that's helpful!
Bonne journée !