How To Writ Up A Check . Voiding a check isn’t that difficult. This is the box on the right where you would normally note the value of the check. How to Write a Check A StepbyStep Guide to Filling One Out from clubthrifty.com However, it is possible to include instructions on the back of a check when you write it. Example of writing off an old outstanding check. (if the check is not cashed within a certain number of.