Social media links are set at User level, however as an Admin you can choose to manually update them for all users in your group, for an individual email.

Starting at Admin level and within the email editor, make your social media panel active by clicking on it, and then click on the options icon to see the settings for this panel.

Under the Networks tab, you will find that as a default the Use user account settings toggle is switched on. Click the toggle to switch it off, and manually update the links. Click Save

Remember that this will only affect the links in this particular email. 

If you only want to update the links for an individual user, either just for this email or for all future communications, start by toggling to the users account via the switcher in the bottom left corner of your dashboard, and then see How do I configure my social media links? - User level.