I don't own the folder that did that bend, my brother in law used to work at a place where he had access to an industrial panbrake (also how the ramps its sitting on were bent). That section is actually an off cut from a bench top we folded up quite some time ago. That is why the repair section is made in two pieces, the off cut wasn't big enough to fill it on the top side but had the perfect bend.
The slot is done with the drill two holes and connect the dots method, I do have some tools but nothing quite as elaborate as a mill.
