Is there a way to remove the triangles on this surface? I am new to blender and want to make some modifications to this model for 3d printing.
As a alternative modification I wanted to close the hole on this surface completely. I managed to create a new surface to close the hole, but then I wanted to extrude the new surface to fill the complete wall depth and it did not add depth to it but only moved it around. How can I fill the hole?

X> Dissolve Edges in Edge Select mode or in Face Select mode select the faces and pressFso they get merged. However, a hole always needs to be surrounded by at least two faces - a face cannot have a hole inside in Blender, so you have to keep two edges. See this answer for more information: https://blender.stackexchange.com/questions/210059/is-there-any-way-to-remove-edges-causing-a-loop/210105#210105 – Gordon Brinkmann Nov 06 '23 at 09:44