Find a bolt about 12/13mm thread size position inside bottom bracket shell so the threaded end is on the outside of the frame not add a couple of spring washers and the nut then keep tightening and once it locks up it will grip the cup and hey presto it will come undone
See https://www.cyclechat.net/threads/1966-dawes-debonair.236653/page-2
I’ve used this method (someone else on this forum recommended it) and used a breaker bar to get some proper leverage and off it popped.