to change collation for system database SQL Server 2017

The Microsoft Books Online for Set or Change the Database Collation explain how to do so, specifically how to in SSMS in the section Using SQL Server Management Studio. Alternatively you can script it as well like so:

ALTER DATABASE DatabaseName  
COLLATE French_CI_AS;

If neither of these options work for system databases, then it’s not possible to do so without running the installer or rebuilding the system databases.

Either way, I would advise being careful with changing the collation of the system databases as you can run into a number of issues if not done properly. For example, a case sensitive collation that needs to interact with a case insensitive context can clash and produce errors. Also using the COLLATE function to compare between two different collation contexts can result in cardinality estimate issues.

Also, please note that if you set the model database to a collation different from the server’s collation then all newly created databases will take the same collation as the model database and ignore the server’s collation.