Tolex is a protective vinyl covering for guitar and bass amps and cabinets as well as for guitar cases. It sometimes gets ripped or rubbed and must be replaced.
Peel off the damaged Tolex. If you can find an edge, you can slowly rip it off or use the hair dryer to melt the glue underneath. Most Marshall amps will need to have the bottom Tolex replaced; the Tolex on the edges of cabinets seems to wear out first.
Remove the old glue by sanding the exposed wood. The glue will stick better and the new Tolex will last longer if the surface is clean.
Cut a piece of new Tolex to fit the area of replacement.
Apply glue to the bare wood with a putty knife. Do not over-apply, as the glue will be difficult to remove if it gets on other areas.
Place the new Tolex on the surface, smoothing it to remove any bubbles or wrinkles.
Remove the old Tolex near a seam, if possible, which makes the repair less obvious. Consider replacing all of the Tolex, not just the damaged part, to avoid a patchwork look.