gmail password change
How do I change my gmail password?
MacBook Pro 13″, macOS 10.13
Question marked as
https://support.google.com/mail/answer/41078?hl=en&ref_topic=7065107
Afterwards, you will need to change it in the Mail app if you use it there. You can disable the account. When you re enable it, it should ask for the correct password. If not, delete the account and then re enter it with the correct info.