The left turn signal stays on until you switch it to the right side?

The turn signals are controlled by the BCM which sounds like it is going out. Here is a guide to help you do a CAN scan to confirm the problem and I have included how to change the BCM out, you can get a preprogrammed unit by searching Google or Ebay.

You can get a CAN scanner (Controller Area Network) which will work on most cars from Amazon.

Here is a video to show you how:

https://youtu.be/u-4syLc-ifQ

and

https://www.2carpros.com/articles/can-scan-controller-area-network-easy

And this can help as well:

https://www.2carpros.com/articles/how-to-replace-a-bcm-body-control-module

Check out the images (below). Please upload pictures or videos of the problem so we can see what's going on.

That scanner will not do a CAN scan unfortunately so it can see if the BCM is having an issue.