Reasons why you are unable to connect your new Android phone to your Gmail accounts:

• You've misplaced your password.
• You've forgotten your sign-in username or email address.-To retrieve your username, go to the username recovery tool. Pay attention to the directions. You'll require: The account's phone number or recovery email address. The account's complete name. Verify that it's your account: Enter the code delivered to that phone if you entered a phone number. If you used a recovery email address, it should look like this: Check your mailbox and enter the code from the Google email you received.
• Your username and password are correct, but you are unable to log in.
• You believe your account is being used by someone else.
• 2-Step Verification is causing you problems.
• You can't use a text message to reset your password.
• You utilise a Google Account as part of your job, school, or other organisation.
• A child under the age of 13 cannot sign into a Google Account.
• You can't use a third-party service to log in.

Read More: Why can't I connect to my Google account on an old Android phone?