Hi there @alex, and welcome to the forum!
Here's a nice short tutorial from another forum member on how to use the table's changeSetArray together with Retool's GUI. Also, see here my post to another user with regards to primary keys and the event trigger you may want to choose (e.g. save button vs a change cell)
You're currently using selectedRow which won't show the edits made to fields within the row.
If you aren't using it already, I find right clicking on any component and selecting "view state" really helpful to understand all the variables I can use across my apps and components.
Hope this helps!