The outside frame will ping off. Firstly try a thin knife in the line between the frame and the central socket body to lever it up a little and then slide the knife in around the back between the frame and the metal face of your unit.
Once this is off you will find 4 small screws holding the corners of the socket body. They are usually No 1 pozi headed, about 12mm x 2.5 mm. You may find another 1mm thick edge on frame surrounding the central socket. This needs to be very carefully pinged off.
Once you undo the 4 screws you should find on all mains voltage fittings, such as this socket, will have a spray can top type shroud for your protection.
I have used this company for what now seems many years for my CBE electrical bits.https://clearcutconversions.co.uk/produc...ampervan-parts/
The attached may also be of use.

Colin