How do I input my turbotax license code into the app

There is no license code for the TurboTax online editions.

If you purchased the TurboTax software either as a CD or Download, install the software on your personal computer and when the application is opened you will be asked for a license code.

See this TurboTax support FAQ for the license code - https://ttlc.intuit.com/community/tax-topics/help/i-can-t-find-my-license-code/01/852973

I purchased my Turbotax Home & Business from Costco and have a license code. When I go to install my download, enter the license code, I receive an error message to re-enter the code...

Assistance with your license code has been provided by clicking here.