How to reset a user's password?

I don’t see any “forgot my password” option on the log in screen. My pod is not open for registration, if that matters.

I also don’t see an option to reset it in the admin user panel.

How can I reset a user’s password if they forget it?

Resetting passwords requires that your pod is able to send emails, if you setup mail sending the reset password link should appear on the sign in page.

Do you know how you can configure my pod to send email? for this

Only the admin of a pod can configure it to send emails. You would need to contact the admin of your pod for this. Most pods are configured to send notifications by email.

If your request is for you to be able to use your diaspora* ID as a personal email address and to send and receive personal emails from your diaspora* account, I believe this is (or, at least, once was) possible, but it is something that very few podmins set up. You could ask your podmin, but the chances are that they won’t want to do this.