This can be tricky especially when a check has been outstanding, but shows up on prior reports. You cannot just go in and void the check. This will throw off all reports. If you are the boss and do not provide reports to anyone, then yes, you can just void the check and be done with it. To do this, right click on the check while in the check register. Choose "edit" check. When the check comes up, click on edit at top left. Choose "void" check.
If monthly reports are provided, then this is not suggested. A voided check in the month it was written will throw reports off balance and cause them to be inaccurate. To void a check, you need to see what account the check was originally posted to. Then, make a deposit. The account to use is NOT income. Use the account that the check was originally posted to. Next time you reconcile Qbks to your bank statement, you will need to click the check off as having cleared the bank, but also click off the deposit you made to offset this check. This will wash each other out and your reports will be accurate.