I purchased TurboTax Premier CD/download at Costco but do not have a CD drive on my computer. What do I need to do to download the software to my Windows 10 device?

You will have to contact Customer Support to request a download.

To call TurboTax customer support

https://ttlc.intuit.com/questions/1899263-what-is-the-turbotax-phone-number

They are available from 5 a.m. to 9 p.m. Pacific time as of Monday, January 8, 2018

Read the packaging on the Costco CD box carefully.

In previous years, either printed somewhere on the box, or on a paper insert should be the information required to download your program.

If you have trouble contact Costco (concierge) directly.