My brakes do not lock.wheels out

Can you tell us a make and/or model number? A couple of pictures showing the brake mechanism might help too.

Often, on this type of equipment, a screw will loosen through normal usage. Have you checked to see if there are loose parts on the braking mechanism? If nothing has fallen off, the fix may be just a matter of tightening up loose screws. The only problem you might have with this fix is finding the right type of tool to turn the screws as the screws may not be plain old Phillips heads. Let us know!

https://walkerforseniors.com/how-do-roll...

If the problem is the breaks have loosened, this gives instructions on tightening them