Has your mechanic backed the adjuster off? There should be a rubber bung on the hub facing part of the disc, removing this will allow access to the shoe adjusting mechanism which is located at the 6 o’clock position behind the drum. It is a cog wheel which once located can be flicked around to back off the shoes with a screwdriver through the hole where the bung was.
In other words turn the drum until the bung is at the six o’clock position, remove the bung, shine a torch through the whole to locate the cog and flick the adjuster cog to loosen off the shoes from the drum, if the drum tightens up flick the adjuster the other way.