Thanks for reaching out. To know install motion graphic templates via Premiere Pro, have a look at this article: Use and customize Motion Graphics templates in Premiere Pro
If I understood correctly, you are using Mac and you are looking for the Motion Graphic Templates folder under system library. You have to look for it under the User Library.
In the finder menu; Go > Go to folder
The path would be:
~/Library/Application Support/Adobe/Common/Motion Graphics Templates/
Note: Adding tilde symbol(~) is important for accessing the user library
Let us know if it works.