Once you get registered, here are the steps to update your profile. Once you're logged in, you're going to click on the gold person icon. From there, you click the arrow next to "My Account" and a drop down menu will appear. Then, click on "Community" and you can update your bio, profile pic and any social media links you may want to include. I've also included a link to a screen recording below, and a screenshot of the arrow I'm referring to.
Since you already have an account, you can open the app or website and click on the gold person icon on the top, click the middle button that says "login" and just login like you normally would with your existing email and password. Once you're logged in, it brings up your account information and you can click on the gold person icon again and then choose "Community Account". It'll take you to a screen that says "Register New Community Member Account" and you just fill out the information on that page, agree to the Community Member Registration Terms and Conditions, and click "Create Community Account" and you're good to go! I've included a link below, to a screen recording where I've set up my own existing account and registered it for a new community account, you can find it HERE