If this is money that was supposed to be in your Roth IRA (because some security lost money due to fraud etc, and this is the settlement for growth you would have had), then:
If you want to put the money back into the Roth, I believe you have 60 days from receiving the check. It is not required that you endorse and forward the exact same check, you can write a check or make an electronic transfer from your bank account as long as it within 60 days. However, I don't know the magic words to tell the IRA to accept it as something that is not a regular contribution -- I will ask for another expert. @dmertz
If you want to keep the money, or it is after 60 days from when you got the check, then I would consider it to be equivalent to a regular withdrawal, which is non-taxable in your situation. Don't report it on your tax return, but keep the paperwork explaining the money for 3 years in case of audit. (**If you get a 1099-R or 1099-INT you may need to report it and then zero it out, you can post back later and ask for instructions if you get a 1099.)
