Do not have MAC or Windows how do I amend rejected 2018 return?

If the return was not successfully filed (rejected) then you do NOT amend it ...  you correct anything that was the reason for the rejection  and print, ink sign and mail it in. 

How to prepare a prior year return
https://ttlc.intuit.com/community/using-turbotax/help/how-do-i-prepare-a-prior-year-tax-return/00/25...

Or If you have a simple return You can fill out the blank forms for free.
Here is the new IRS 2018 Form 1040
https://www.irs.gov/pub/irs-pdf/f1040.pdf
And instructions https://www.irs.gov/pub/irs-pdf/i1040gi.pdf
2018 Tax and EIC Tables https://www.irs.gov/pub/irs-pdf/i1040tt.pdf

IRS 2018 Schedules 1 thru 6
https://www.irs.gov/pub/irs-pdf/f1040s1.pdf
https://www.irs.gov/pub/irs-pdf/f1040s2.pdf
https://www.irs.gov/pub/irs-pdf/f1040s3.pdf
https://www.irs.gov/pub/irs-pdf/f1040s4.pdf
https://www.irs.gov/pub/irs-pdf/f1040s5.pdf
https://www.irs.gov/pub/irs-pdf/f1040s6.pdf

Don’t forget your state. And you will have to print and mail your returns.  So be sure to attach copies of your W2s and any 1099s that have withholding on them.  You have to mail federal and state in separate envelopes because they go to different places.  Get a tracking number from the post office when you mail them for proof of filing.