I can think of only two solutions, good and not so good.
Good: Replace the entire cooler with an aftermarket unit or the card with newer unit
not so good: (IF YOU PROCEED YOU ARE DOING SO AT YOUR OWN RISK AND WILL NOT BLAME ME IF THE WORST SHOULD HAPPEN)
each fan has 9 blades, Remove two more blades so the fan is balanced, damaged blade, then two good blades then damaged blade.
if you can remove the 3 blades from the fan you should be able to use it with diminished airflow until such a time as you can replace the cooler or the entire card. cheapest short term solution I can think of.
https://www.arctic.ac/us_en/products/cooling/vga.html
my suggestion for cooler