Hi Susan,
This can be done by using the "getDataAsString()" method of the data source that the chart is using. If you would like this change to be made to the text box every time you assign a value to the variable of the data source, then the following syntax can be used within the "on Result Set Change" event of the data source itself:
TEXT_1.setText(DS_1.getDataAsString("<Name of the Measure>",{"<Name of the Dimension (Year)>" : DS_1.getVariableValueText("<Variable's Technical Name>")}));
Thanks and Regards,
Eshwar Prasanna