If you purchased the software at Costco you purchased desktop software. One of the choices in the file section is to file by mail. That is what you need to do. E-filing has been closed since October 15, A 2018 return cannot be e-filed now. Print it, sign it in ink, and mail the return. It will print with mailing instructions.
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/state received the return.