I'm not an expert, but I don't think you can. They are 2 different products.
Also, if you are expecting to be able to access the return you prepared on your desktop online, you are mistaken. The data from your desktop is not available online. If you used the online product, you would have to start all over.
I suggest you file an extension request.
More information and how to do it is available here:
https://www.irs.gov/forms-pubs/extension-of-time-to-file-your-tax-return
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