The "xxxxx" indicates that the field you clicked is a TEXT field, probably a formula.  When you click on the field, the identity of the field will appear in the lower left corner of the Report Designer window, with the name of the field and the formula name appearing in parentheses.  Then go to Tools > Formulas > Design Formulas if the field is a Design Formula, click on the formula name, and then click "Change" in the options buttons to the right.  Make the changes required and click OK.  Be sure to observe the syntax for a text field: it must be enclosed in Quotation Marks (" ").

Thank you!