2021 model - original Gen1 ZS EV then with the black front grill and large chrome MG badge ?.
I guess you require the light assembly mounted in the rear quarter panel and not the light assembly mounted in hatch back itself ?.
I think you will be looking at purchasing a complete back light assembly then because the coloured lenses are not removable.
I would call and request a price from an MG dealer first, then compare this to the price from an on line EV breakers price ( e.bay ).
A quick check reveals that these can be obtained for prices at around £40 - £100 second hand of course.
I expect that the Gen1 light assembly will be less expensive than the Gen2 model, as the later model has a part LED set up.
Removing the complete light assembly in the rear quarter is covered in the owners manual.
Here is a video covering how’s it done.