I mended our blinds and fly screens when they ripped at the bottom. There is usually some extra blind on the roller, pull down the blinds as far as you can to check.
If so stop them from rolling back up with a clothes peg either side. I took out the bottom bar from it's runner. Inside the bar,(you have to remove one end stop) there is a small plastic rod that the blind is folded over. Make the end of the broken blind tidy and then fold it over the rod and sew in place. Slide the folded blind back into the bottom bar and insert back in the side runners.
Hope this helps.
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