If a player of your team has not activated his account after your invitation, then the email of the player is not shown on the team roster or on his profile page. You can thus easily modify the email address and then send a new invitation to join the team at the new email address.
If a player has already activated his account and joins the team further to your invitation, so its email address is shown on the team roster or on his profile page. But be careful, you can't change his email anymore. Indeed it's his email address, which he can also use for other teams. So, if the player wishes to change his email, he just has to connect with his current email and his password to reach his profile and modify his email itself. But you can ask him to change it if you know that his former address is not active anymore, for example.