Hello, I think it would be best if you order a completely new operator rather than just replace this one part, as it would act as a better replacement. If you wish, you can upload a picture of the whole operator and we can identify what you would need.
Now, here is how I would install the bracket:
First. drill out the old rivet, then find a small solid piece of metal--or something hard--that is about 1" thick to lay the operator arm on.
Now, assemble the nylon bracket and rivet to the arm and place the assembly on a metal block. With a hammer, whack the rivet to start spreading it.
Squeezing this between a piece of metal (like a mallet) and an air hammer works great. You can do this in place without having to remove the window trim/crank. I have fixed five cranks this way so far; no issues.