The "right" way to fix it is to find a donor fuse box and swap over the contacts, once burned like that, you'll have repeated problems.

The next best way to fix it is to get an in-line fuseholder and tie it into the wiring outside the fuse box. Make sure to label your fusebox legend if you do that.

You can try to salvage what's there by getting the metal off. You'll need to use some carbide sandpaper and some elbow grease. If you can't get it down to bare metal, you'll have to do something else.

While you're in there, replace ALL of those crappy aluminum fuses. They cause LOTS of problems.

__________________
Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]