If your USB drive is not readable by the PC, CHKDSK will likely not work on the USB drive. But, there’s no harm in running CHKDSK to see if it can find and detect errors on the drive. Just remember to first create a backup of your data.
Run Command Prompt as administrator.
Type chkdsk X: /r (where X: is the drive letter of the USB) and press Enter.
Wait for CHKDSK to detect and fix the errors.