I have just removed the lighting wirings inside the PVC trunking which has not been used for more than 10 yrs. I need to remove the PVC switch as well. But the problem is that white PVC switch is nailed onto the wall using concrete nails and I do not know how to remove them.

No way to cleanly remove them.

Is to use flat scewdriver and hammer/wedge them out, which means the PVC box also will get spoilt.

Then need to use putty and paint to cover up any holes/ scar marks.

U can try using a hammer and screwdriver and hammer the nail loose, but that is likely to create more cracks.

easier way perhaps can wack that nail further in and plaster it over.