Click this link for more info on How to Report Inmate Income.
If you don't have Power of Attorney for this person, it would be well advised, however, to ask permission from the prison / jail authorities on mechanically how you are allowed to do so (e.g., e-file or postal mail; or from within the facility itself or with outside assistance).
They should be permitted to file a tax return as a matter of federal law, but the procedure may well vary by facility, so that's why it's a good idea to ask someone first.
This link has more info on Filing for an Incarcerated Person.
[Edited 3/3/2021 | 10:43 am]
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