You create your login credentials when you register within the AgroCares app. You define your password yourself. Your username will be the same as your email address.
If you get a new email address, then you can change the contact email address that is used to e.g. reset your password.
You can not change your username. When you update your email address, then your username will stay the same as the old email address.
You can update your contact email address via the AgroCares Portal: https://portal.soilcares.com/.
Open your account details via the green menu in the upper right corner of your window.
Your Account menu allows you to change your contact email, your password and other account details. Click "Update Account" and your new email is saved.