The answer to 'how to unclog repiping' is to use a plumbing snake or auger to clear the clogged pipes. First, locate the access point to the clogged pipe, which is usually under a sink or in the basement. Insert the end of the plumbing snake into the pipe and turn the handle to feed the cable through the pipe. Continue feeding the snake until you feel the obstruction, then turn the handle in the opposite direction to pull the snake back out, bringing the clog with it.
If the clog is severe or the pipe is damaged, you may need to call a professional plumber to properly diagnose and fix the issue. Repiping, or replacing the entire plumbing system, may be necessary in some cases.