The PAR files and rar files should be in the same directory by default (I'm assuming they already are)
D/clicking on one of the PAR files should launch Quickpar, which in turn should check the integrity of the rar files.
i.e. whether any blocks are missing (incomplete) or any
files are missing.You can only do a repair if you have enough PAR files to cover missing blocks/files.
Below is what you would see if you didn't have enough PAR files
edit: make sure your version of Winrar is up-to-date
PAR & PAR2 FILES