This painting was punctured ( top photo) and here you can see the patch on the reverse side of the painting. I was told by folks who do this for a living… all you need to do is ; smooth out the fibers which were ripped, lay the canvas back as it should look, use any archival glue such as “YES” or any medium (used in collage) such as matte medium for acrylics to hold a new piece of canvas onto the back side of the painting. Then allow this patch to dry over night. When everything is dry, you will repaint this area and later use retouch varnish to give the front of the painting a consistent look. After six months the painting should be varnish.