I have recently done those two corners of my dash albeit in leather but doing it in either MB Tex or leather, should be the same.
My dash corners had excess material that wasn’t glued to the triangular piece that has the screw in it.
The dash piece was placed in position and the excess material was lifted up out of the way for the screw to be fitted to hold the dash piece. The leather or MB Tex is glued over the top of the screw, stretched and gets fitted underneath the piece of chrome that goes down the lower part of the A pillar (S shaped piece). Both this leather piece and the windlace get fitted underneath that chrome piece so both ends of the leather/MB Tex are hidden.
I’ve attached a pic of me pulling the leather over to show you what I mean.
When I purchased my car, there were pieces of tissue box cardboard covered in vinyl in each of these corners. Definitely not correct, never mind the fact the dash had been vinyl painted black when it should be blue.
I’ve asked a similar question of the forum a while back so you should find some other pics on that post. When I find it, I’ll reply with it here.
Doug