If you cannot use a computer from a trusted friend or relative for amending your tax return then you can complete the return manually. An amended tax return can only be printed and mailed, it cannot be e-filed.
IRS Form 1040X - https://www.irs.gov/pub/irs-pdf/f1040x.pdf
IRS Form 1040X instructions - https://www.irs.gov/pub/irs-pdf/i1040x.pdf
IRS website for free federal forms, schedules and instructions - https://apps.irs.gov/app/picklist/list/priorFormPublication.html
IRS website for where to mail the amended tax return, Form 1040X, click on your state - https://www.irs.gov/filing/where-to-file-paper-tax-returns-with-or-without-a-payment
