Using a transcript to file

What do you mean by "transcript"? Do you mean that you have your father's SSA-1099 forms showing the Social Security benefits that he received? If Social Security was his only income he was not required to file tax returns. There is certainly no point in filing them now.

The usual meaning of "transcript" in relation to taxes is a document from the IRS that lists the information from a tax return. But that's for tax returns that were filed. If you have a Tax Return Transcript from the IRS, the tax return has already been filed.

If your father's only income is Social Security he is not required to file a tax return.   What transcripts are you referring to?   If your dad has been getting Social Security he receives a SSA1099 every year in late January.

And....the current online software is only for 2020 returns.   There is not a way to use TurboTax to file a past year return for free even if you have taxable income to enter.   

A past year return has to be prepared by using the purchased CD/download software.  And the return has to be printed, signed and mailed.   It cannot be e-filed.

Please explain why you think you need to file returns for Social Security for your father for the past three years so we can understand and be more helpful.  It is not clear what you are trying to accomplish.

if he was not married and Social Security was his only income for those years he has no filing requirement.

if he has a filing requirement you must buy the desktop software for any year prior to 2020. only 2020 is there a free online edition available.