Box 13
This box has three sub boxes designed to report pay that is not subject to federal income tax withholding, if you participated in an employer-sponsored retirement plan or if you received sick pay via a third-party, such as an insurance policy.
These boxes will be checked or left unchecked by your employer. If it's checked, you also check the Box in TurboTax, if it's unchecked, leave it blank.
You can remove the check by simply clicking the box again.