My idea to solve it is to trim a little surface 'A' using a router, but I am not sure from which direction to do it and with which type of router bit. Is this a good approach?

A trim router is a great finishing tool for when you're done with the broad strokes and need to get into the details. Here's what you need to know.

This video demonstrates the complete process of making door casings from pine wood using a manual router, showcasing various techniques ... Perfect for DIY enthusiasts and woodworkers looking to ...