Activists are calling for a co-ordinted boycott on 14th and 15th December of the department store Marks and Spencer.
x.com/MMYang434/status/1865835236820390085
There are easy print leaflets you can hand out outside your local store. See this thread
ovarit.com/o/Activism/631093/leaflet-campaign-for-single-sex-changing-rooms-at-marks-and-spencer
Or you don't want to put yourself in the public eye you can print them and post them to the chairman, the manager of your store (or several stores) and perhaps your local and regional newspapers too?
The chairman is Archie Norman and the Chief Executive Officer is Stuart Machin.
The Registered Office of Marks & Spencer
Marks and Spencer Group plc Waterside House 35 North Wharf Road London W2 1NW
Even if you're outside the UK but you visit M&S stores when you come here you could still write and say you want single sex facilities for toilets and changing rooms.