"over a call" vs "on a call"

I will explain about the project over a call

I will explain about the project on a call

I have read here that over can be used as during

So is explain over a call correct?

which is the correct usage?

Yes, in some cases "over" can be used as during, but this is not one of those cases. I would suggest "in a call". That conveys that your explanation will be "in" (that is, part of) the planned call. And there's nothing wrong with "during the call". The phrasing "on a call" carries the idea of being engaged in a call, but it's used this way: "wait a minute, I'm on a call" (he is busy talking on the phone).