Use a protractor to measure the exact angle of the corner. For ease of discussion, let's say your corner is 84 degrees. Halving that will give you the angle you need to cut the framing boards (relative to the outside edge). In this example, that would be 42 degrees.

Thank you. I will order one of these corner angel products. They look promising🤞

I found this angle finder to be helpful. Once I cut one board, I could also flip it against another board to mark where I need to do my second cut. The only challenge was to get a nice clean cut with my circular saw.