You are using TT online, not the download. Why do you need the download?

If you want to switch to the Desktop download program you can try asking them to switch you.

Contact Customer Service 5am-9pm Pacific Time 7 days a week
<a rel="nofollow" target="_blank" href="https://support.turbotax.intuit.com/contact/">https://support.turbotax.intuit.com/contact/</a>  

I want to file my 2017 tax return, but apparently you can only do that with the download version.

Oh,  sorry yes. Did you pay for the 2018 Online Deluxe?  You can still use it for 2018.  

You can buy the 2017 program here,
https://turbotax.intuit.com/personal-taxes/past-years-products/

Did you start 2017 online last year?  You can download the .tax2017 online file to finish in the Desktop program.

Yes I paid for 2018 online deluxe. I did not start a 2017 return. I would like to file 2017 return. Does that mean I ALSO need to pay for the 201$ downloadable version?

Yes.  You need to buy or pay for each year separately.  Do you have a full Windows or Mac computer you can install the program on?  Or you can fill out the blank forms for free.

If you have a simple return, you can fill out the blank forms by hand for free.
Here are some blank forms & instructions for 2017
1040 <a rel="nofollow" target="_blank" href="https://www.irs.gov/pub/irs-prior/f1040--2017.pdf">https://www.irs.gov/pub/irs-prior/f1040--2017.pdf...
Instructions <a rel="nofollow" target="_blank" href="https://www.irs.gov/pub/irs-prior/i1040gi--2017.pdf">https://www.irs.gov/pub/irs-prior/i1040gi--2017...>

1040A <a rel="nofollow" target="_blank" href="https://www.irs.gov/pub/irs-prior/f1040a--2017.pdf">https://www.irs.gov/pub/irs-prior/f1040a--2017.p...
Instructions <a rel="nofollow" target="_blank" href="https://www.irs.gov/pub/irs-prior/i1040a--2017.pdf">https://www.irs.gov/pub/irs-prior/i1040a--2017.p...>

1040EZ <a rel="nofollow" target="_blank" href="https://www.irs.gov/pub/irs-prior/f1040ez--2017.pdf">https://www.irs.gov/pub/irs-prior/f1040ez--2017...
Instructions <a rel="nofollow" target="_blank" href="https://www.irs.gov/pub/irs-prior/i1040ez--2017.pdf">https://www.irs.gov/pub/irs-prior/i1040ez--2017...>

2017 Tax Tables <a rel="nofollow" target="_blank" href="https://www.irs.gov/pub/irs-prior/i1040tt--2017.pdf">https://www.irs.gov/pub/irs-prior/i1040tt--2017...>
Publication 17 Tax Guide for 2017 <a rel="nofollow" target="_blank" href="https://www.irs.gov/pub/irs-prior/p17--2017.pdf">https://www.irs.gov/pub/irs-prior/p17--2017.pdf</a>

Prior year returns can only be printed and mailed.  When you mail a tax return, you need to attach any documents showing tax withheld, such as your W-2’s or any 1099’s.  Use a mailing service that will track it, such as UPS or certified mail so you will know the IRS received the return.

And don't forget state.