1. Sign in to Google Domains.
  2. In the left-hand navigation menu, click My domains.
  3. Click the DNS tab  for the domain name.
  4. Under Name servers, select Use custom name servers.
  5. Enter a custom name server in the Name server field.
  6. Click the + button to add every other name server.
  7. Click Save to save your name servers.

 

Please see Google Domains for more info:

Change Nameservers: Google Domains