how do i reset my mail password

Changing any such password is always at least a two-step process.

First, log on to webmail (a very fancy term for looking at your mail in a web browser). Do whatever the email provider requires to change the password. once successful, continue to Mail on your Mac.

Second,

Mail > Preferences > Accounts ...

... and select the amount in question, and change its password to match the change you just made in webmail.

your accounts page may be different.

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Then use Mail > Window > Connection Doctor

you should see all green lights. if any are still red, click on them and you will get quick access to the password settings for the receiver or sender server for that account, and can enter the password there.

With whoever is your email provider.