What credit? Is it the $10 credit toward efiling a state return? I think you may have used the Online version instead of the Desktop program you should have installed.
Sorry you can't apply the Desktop CD/Download program purchase to the Online version. (The App is just a portal to the Online version.) They are separate prices and work different. You have to pay for online and try to get a refund for the Desktop program. Or switch to your program.
To Continue in your Desktop program......
You need to install the program on your computer and move your online return to the Desktop program. You can move your Online file to the Desktop program and continue without paying for Online or needing to reenter your info.
How to install the Desktop Download program
https://ttlc.intuit.com/turbotax-support/en-us/help-article/product-delivery/download-software-turbotax-com/L7u9oLEkq_US_en_US
To continue in the desktop version see this…….
https://ttlc.intuit.com/community/choosing-a-product/help/how-do-i-switch-from-turbotax-online-to-the-turbotax-software/00/26129