Underneath preparation and sealing.

Passed the mot today car has never been welded and I've owned it17yrs,anyway had one advisory saying surface corrosion underneath so would like to get this sorted.It's probably down to it sitting in the garage most of the year,would a body shop sort this out I don't want tons of underseal sprayed over what's there I would want it all prepared then sealed.

Get on your back with a grinder, grind the area affected, zinc prime it then tetroseal it or similar undersealer will do.