Gary

Show where you define the variable.
Is it in a global module? How do you assign data to it?
How do you read data from it?

You cannot use a global variable as the control source.  You can, however, use a VBA function as the control source.  See the picture below.  The VBA function used in this manner also cannot contain any VBA elements: e.g., MyFuncton(Forms!Form1!Field1), or MyFunction(GlobalVar).  It can only use literal values in the argument, MyFunction(100), or no argument.  In short, you cannot have any VBA stuff on the property sheet.  VBA code can only be run by a VBA module.  A property sheet cannot run any code, because it is just a storage container of properties.

If you want to "dynamically" assign values to a control, make the control unbound (i.e. blank control source), then use VBA code to assign values to it when needed.

Power Apps can do what you try to do: put variables on the property sheet.  When variables change values, so do the properties, automatically, without needing any extra code.  Power Apps is "low code" platform, so it is designed that way.  Access and VBA aren't.

I couldn't get the Function() method to work either. The function retrieved the data from the text box fine'I tested that by displaying it with a MsgBox. But putting the function as the control source for the MailingLabel control on the report didn't work. So, on to Plan B. And that was adding a field to my HelperT table, then using SQL to update the field in the table, then using a DLookup as the control source for the MailingLabel control. See attached. This may not be the most elegant solution, but it is working. Thanks for your response!

I, like Adam, would use TempVars.