To set up a label to print data based on your response to a prompt (i.e., prompts for item number, and then prints a label for that item number with the corresponding description pulled from the external data source) add a filter, select the column to prompt, and set the value to = <Prompt>. When saving the filter, it will prompt for the value twice, click Ignore both times. It will give an error because it won't be able to apply the filter with no data, then return to the label design screen.
When you print the label, allow it to print All filtered records from the source. It will then prompt for your value. Either type it or select it from the drop down list, and then it will print that label.