Essentially, you have two choices:
1) Carry back the entire amount of the NOL from 2020 to 5 years before the NOL year (2020); or
2) Waive the carryback period and carry the NOL forward indefinitely until it is fully absorbed.
See https://www.irs.gov/publications/p536#en_US_2020_publink1000177354
Regardless, you cannot start the NOL carry back in the 2017 tax year (if you choose to carry back the NOL).
Thanks so much, I really appreciate that...I started my business in 2015, so I would carry it back to 2015, but end up using all of it probably on my 2017 return as I owe $1,800 on that year still.
How do I do that? Can I do it myself? Do I do something special with my 2020 taxes? Do I have to amend past years returns?
You should probably seek professional guidance for this process as it is not exactly simplistic.
There is an example and additional information at the link below.
https://www.irs.gov/publications/p536#en_US_2020_publink1000177383
Can I attach form 1045 to TurboTax and file it electronically with my 2020 TurboTax filing? Or do I need to print and mail it all together?
TurboTax does not support the calculation of an NOL nor does any edition of the program include Form 1045.
See https://digitalasset.intuit.com/DOCUMENT/A6QrdFCgW/010421-2020-unsupported-calcs-L1FQfTTgn.pdf
As a result, you would have to prepare Form 1045 manually, combine it with your TurboTax return, and then print and mail them together.