"My personal Gmail account is the default. How do I set my company Gmail the default?"
SHORT ANSWER: First sign out of all accounts, then sign in with the first one you would like to make your default.
MULTIPLE SIGN-IN: Google’s “Multiple Sign-in” accounts feature is very helpful in many ways. Many people have multiple Gmail accounts. Here is a simple way to set your most company Gmail account as a Default account for your browser.
1. Go to Google site (Google.com or gmail.com) use non-private browser for this to let the cookies set in.
2. Then Log out of all the Gmail accounts your sign-in to, this can be done by clicking on your avatar icon on the right top side corner on the Google/Gmail page and choose to Sign-out.
3. Now you just have to go to the Gmail log in page and log in with the account you want to set as your default account. The account you logged into at the very first will become your default account till you stay sign-in.
4. When you got log-in to your primary account which you wish to set as your default Gmail account. Go to the avatar icon again and click on it, a dropper will display click on the “Add Account”.
5. Now you can add as many as other Gmail account in your multiple account list.