Individual elements of an array or object do not have formats. Most data types do not have formats that can be controlled by the user (but datetime and duration objects can be controlled per variable)
When you talk about clicking on a cell you are talking about using the Variable Browser. You can go into Preferences to change the default format used by the variable browser.
Changing the format in the variable browser, or by using the format command, never affects the content of the variable or how it compares to something else.
Your problem is that the value you are searching for does not exist in the array.
You should look at ismembertol()