Injection question

How long do you let an injection site rest before hitting it again? I'm doing tren 1ml every day.

As long as you can bro. Rotate so that you don't get scar tissue buildup. Although if you have frequent injects due to your dosing strategy, it's not unheard of to hit the same parts every few days even when rotation all over. I've hit quads ED before, just an example.

Here's what I'm trying to do. I don't have perfect symetry, but I'd like to improve it if possible during the next three weeks by injecting into the lagging bodyparts. For example, one side of my chest is fuller and denser than the other. So I'd want to inject into the smaller side and skip the other pec. I have four different sites in mind, right pec, left lat, left delt, left tri. Would every fourth day be ok for these?

Somehow, injecting towards my heart just scares the shit out of me.....

I think it's debatable as to whether or not that will actuallly work. Sometimes I think it does, like in my bis, but I'm not totally convinced the whole muscle fascia stretching theory actually works for spot injecting. I'd be more inclined to believe in the localized training than the localized injecting.