To change your default gmail account then follow these steps.
Access the Gmail page as usual and click on the icon on the top right that represents the where you are
Close the session of all the accounts that you have open using the button called Sign out. Do this step for which you have the credentials activated
Now reload the Gmail page and you will be asked to enter the username and password of the account, choose the ones that correspond to the one you want to act by default. Once this is done, you can use the rest, since you will not lose the established configuration unless you take the steps indicated again
Follow these steps and you can easily change your default gmail account in chrome.