I had the same issue happen on my (guess!) 2018 Model 3, purchased in spring 2019 - so it is just out of warranty.
I filed a mobile service request with Tesla and asked that they cover the fix, seeing as it is apparently a common problem with this model year, with a weak plastic component. Plus, I've never seen a part like this ever break on any other car I've owned.
After my chat (with photo), their initial quoted estimate was around $50 for the visit including the part – but right before the technician arrived, I received an updated estimate at a total cost of $0.00.
Once on site, it took the fellow around 20 minutes to replace the broken part and he left with a handshake.
Thank you to Tesla for doing the right thing!