What Althulas said, take a flap disc and clean back to new metal.
Go to
View: https://youtu.be/_zJW9Thp2ow
and Karl will show you how to hammer form a repair section. It sounds and looks scary when you’ve never done it before, once you jump in it’s not actually that difficult. Forming simple one off shapes in mdf works well. For something tight, use steel, or a mix of steel/mdf. A bolster chisel, scrap steel, hardwood for the counter punch, all work.
To drill the hole, either a kitchen hole punch, or a holesaw from Toolstation, or Screwfix.
I would not advise seam welding it, I would use what’s called “zap and chill”. Essentially a series of tack welds whilst chilling between welds. It means you don’t need to clean quite so far back, melt less under seal and have less chance of fire. Karl on above link will show you how to do that too. I’ve used the technique for years, it works really, really well.