Losing display configuration

Can some kind soul please help.
Since updating to Leap 42 from 13.2 I have been experiencing repeated problems with my monitor display configuration. It insists on changing to the maximum resolution my monitor supports, the result being that the screen is practically unreadable with my failing eyesight.
I was able to reset the display configuration through “K.application menu/Settings/System settings/Hardware/Display and Monitor” which should provide the facility to adjust the display settings and the screen locker. Now I only get screen locker and cannot access display settings.
This problem seems to be linked to updates possibly to Plasma although I am not certain as each time there was an update I would lose display settings and the ability to reconfigure, then along would come another update and I could reset the display again. However since the last update some time ago the loss of the ability to adjust display settings seems to be permanent.
I would very much appreciate being able to read my screen without developing a headache through eye-strain.
If anyone can point me towards any solution (has to be easy and simple for a feeble and ageing brain) I would be very grateful.