Identify when a date is to expire

[Wolfie301]

Hi all, I am new to this forum and have a question that may have been asked before but I cannot find it or a solution. I have been asked by a friend how to set up excel so that when their staff complete a test on a certain day that they can be identify when 5, 11 and 23 months pass as a reminder that the test is expiring and needs to be retaken.
I have looked on the internet but all scenarios seem very complex and not really what is required for a basic elapsed time test. Many thanks in advance.