I purchased home and business key, but I want to do my return online. how do I do this?

No.  The TurboTax desktop CD/Download editions and the TurboTax online web-based editions are separate programs with separate price points.

Why would you want to use the Online editions if you have already purchased the desktop software, which is a far superior product than the online editions?

Sorry you can't apply the Desktop purchase to the online version.  They are separate things and don't talk or sync to each other.  You can move your online return to the Desktop program without paying for online so you don't need to start over.

You can move your Online file to the Desktop program and continue without paying for Online or needing to reenter your info.

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

Or try to get a refund for the Desktop program.