It looks like the rear wiper is a 14" wiper. Assuming you have a compatible style of rear wiper blade, it's easiest to search online to find a 14" wiper rubber replacement. I found this on Amazon for $6.73. You can also get a cut to length wiper refill kit and trim it to size :)

I recommend referring to this guide on Jalopnik to make sure your wiper is compatible before you make your purchase.

Good luck, and I hope this helps!