It’s not a new suit. It’s the same suit he was wearing the entire time.

However, every time we see his suit it is either not a clear shot or his suit is not lit up. When they exit the quantum realm the suits not lit up but it’s really the first clear shot of the suit we get. Then during the shot of them escaping the rumble is the first time we actually see the suit head on and lit up. And yes the suits look completely different with the lights on, but if you look at the shots with Nebula you can see it’s the same suit, because those suits are lit up as well.

But yeah that scene was totally jarring for me too. Because I was like where did he get the new suit. The real question now is since we know it was the same suit he was trapped under the rumble in, then how come he got out of it to help rocket if it was working, or how did they fix it and get him back in it?

Rocket must have fixed it on the way up.