How can I obtain an extra copy of a marriage license after 50 years?

My grandfather recently pasted away and my grandmother is trying to figure out all the bills, etc. Some places require to see a copy of their marriage license in order to transfer his accounts to her. The problem is my grandfather had hidden the marriage license and our family can’t find it. How do I go about getting a duplicate copy of their marriage license after 54+ years?
(They were married in Michigan and were currently living in North Carolina if that helps anything). Your help is greatly appreciated. Thank you so much!

Starting Your Marriage Right: What You Need to Know in the Early Years to Make It Last a Lifetime

• ISBN13: 9780785288527
• Condition: NEW
• Notes: Brand New from Publisher. No Remainder Mark.

Product Description
The Raineys offer an upbeat and practical manual for marriage to guide couples through the challenges they face as they start their lives together…. More >>

Starting Your Marriage Right: What You Need to Know in the Early Years to Make It Last a Lifetime