.. there are fabric adhesives, I'm trying to re attach the seam tape in my rain pants with some, as it comes loose.
I sewed on patches to my sewn together panniers, my Ortliebs stay dry by not having holes in them.
Those bags being thermally bonded hot melt glue or Iron on patches may be an option ,
but the temperatures would need to be controlled to be low enough to not mess up the structure and waterproofness.. .