Sadly, unless you get access to a printer, you cannot file it. A 2018 return cannot be e-filed. It has to be filed by mail. You cannot mail it until you can print it. E-filing for 2018 has been permanently closed since October 15, 2019. Sorry.
If you have income to report on a 2019 return, a 2019 return can be e-filed. The online software is ONLY for 2019 returns.