How to Edit an Array in Firebase Database using the Namespaced API in vanilla Javascript?

I have an array of objects called ‘markers’ in the Firebase Database. How do I edit a single object from the ‘markers’ array using the namespaced API in vanilla Javascript? Do I have to JSON.stringify?

I tried using database.ref[‘markers’].set(, however errors kept appearing such as:
Uncaught Error: set failed: value argument contains undefined in property ‘markers.1.comments.0.user’