To change/add social icons first click on your Username on the top right of AdvisorStream, and then click "Account Settings".
Click on the "Profile & Branding" tab.
Select the profile where you want to change/add your social icon.
On the "Social Media and Website Links" section select which social media you want to change/edit by pasting your social URL into the social media field.
Click 'Save' on the bottom left when you finish.