I bought Premier soft ware at Costco. Somehow I can not install into my ipad. Where do I input the license code on this on line turbotax

Desktop software cannot be installed on an iPad.  It has to be installed on a full PC or Mac computer.   There is not a way to enter the license activation code for a desktop product in Online TurboTax.   The 2 products are not interchangeable.

If you don't have a computer and wish to use Online TurboTax instead, you should be able to get a refund for your desktop software purchase.   See if Costco will refund it (try that first--its the fastest, if they'll do it).  If they won't, then this FAQ tells 2 different ways to request a refund from TurboTax.

FAQ:  How do I request a refund for my TurboTax product?

https://ttlc.intuit.com/turbotax-support/en-us/help-article/intuit-refunds/request-refund-turbotax-product/L834M6uyW_US_en_US