How to fix a disk brak problem i have one rear brak strongre nthan ather

Then you have a fluid flow issue or lack of
brake maintenance issue

You don't meantion the vehicle or any details of
any type of parts removal or checking to see what
condition the brakes are in

The brakes have to come apart once a year to remove rust,
inspect things & lube & there is no reason, if you do that, to
ever have a problem

You could have a restricted rubber hose if they are 10 years
old & not changed,rusted parking brake cables

We need something to go on to suggest something

I will tell you that I have never had an issue in 49 years
of doing brakes & I believe neglect is 95% of all braking problems