Hiya Dave,
I’m not an expert on these matters and there are people with far greater knowledge. I think there are three main components, the rear connection to the brakes, the handbrake adjuster and the cable that connects the handbrake to the rear brakes.
Sounds to me that it’s ever the handbrake adjuster to slacken tension or the cable.
For ease you could look at the handbrake adjuster first, although the issue may lie elsewhere.
Good insight by @ast on link below.
Extra info, incase you need to replace cable
Good luck.