The only way to change someone's e-mail address is to ask that person to change it on their own.
Why can't I change someone's email address?
You started using Productive and invited other people from your organization to join the account. E-mail addresses you entered when you invited people became their credentials. Once they accept your invitation, they will set up an account password.
So, the next time they log in, they will be using that same e-mail address the invite was sent to and a password they had to choose as a first step of creating their account.
That's why you can't change others' e-mail addresses. No matter if you're an admin, the e-mail address works as a username and no one can change it except the person whose account it is.
If they need to change their email address, or you want to change your own, go to Settings > Account and select Change My Email.
A user cannot access his account and we need to change his email! Can you do it for us?
If a user cannot change his email, we will help you out, of course. In such case, contact us using the in-app chat and we can change someone's email for you.