Sign in to the Google account you want to use by default
Open a Google service such as Gmail, YouTube, or Google Drive
Click your profile picture in the top-right corner
Select Sign out of all accounts
Sign back in with the account you want as the default first
Add any other Google accounts after signing in to the default account
Keep using that first signed-in account as the primary account in that browser
If needed, clear browser cookies and sign in again in the desired order