For this situation where you filed as Married Filing Jointly and you are no longer married to the spouse that would have been on the refund check, you will need to call the IRS and speak with an agent - (800) 829-1954
Normally a Form 3911, Taxpayer Statement Regarding Refund would need to be filed - https://www.irs.gov/pub/irs-pdf/f3911.pdf
