How To Remove Recent Welding

without destroying the metal underneath?
Wait, huh? He overlapped your floor pan and ran a bead? There's 3 ways this should've gone down, and that ain't one of them.

1. Fit it properly and butt weld.
2. Flange, bead or spot, then seam seal.
3. Overlap, spot, then seam seal.

Have someone competent check that trans cross member. That is one of the most important structural members of the whole car.