Please carry out the following steps to resolve the issue with Gmail now:
First, open up Gmail on a new window.
When the new account automatically opens up, click on the circled/round icon at the top-right corner of that page and then click "Sign out."
You will then be signed out of that account and taken back to the login page.
There, click on the small "Sign in with a different account" link at the bottom, and then click "Add account."
Next, sign in to your old Gmail account thereafter, and you should be good to go.
If you need more help, please use the Reply box below to continue our conversation.
Otherwise, kindly take a moment to rate my service by clicking on (and submit) one of the five stars at the top of this page - this is the only way that I'll be credited for assisting you today. Thank you.