I've linked a help centre article below that explains how to do that.
Set screen lock on an Android device
For further support with your Android device, we recommend posting in the Android community where experts can better assist.
Just checking in to see if you still need assistance with this issue.
Please let me know if you need further assistance.
P.S Thank you for your help, @David_K!
Just checking in one last time to see if you need anything. This thread will be locked in 24 hours.
At this time, I'll go ahead and lock this thread. If you're still experiencing problems, feel free to start a new thread and we'll be happy to help.
Google Nest Help Center
Chromecast Help Center