How do I extend these 2 identical models to they intersect?

I have 2 identical models, one is vertical and the other is horizontal at 90°. I want to extend them so they both meet at a 90° mitered corner. I cannot figure this out and it seems like it is something that should be very simple.


My gosh why didn’t I think about that? :man_facepalming:
Thank you so much for the help!