1/4 install snafu

Ok, if you used a MIG welder, it's gonna be hard to fix. Because, The MIG welding process leaves a stiff allmost non malleable, Joint. If you TIG Welded it your in luck, it leaves a "soft" weld. Just, Beat it into place.
Now, Either way, I would suggest heating the indented area with a torch (orange red) banging it out close n follow with minimal filler.

Hope this helps, Eric