There is 2 ways to add social links to your templates. Either through the Dashboard or in the Builder.
From The Dashboard:
You can add the URLs for your social icons in the Company Settings of your dashboard.
You can get here by clicking "Settings"
Then click "Company Settings"
Scroll down to "Social Links" and here you will find the area to add your social links. Make sure you to click "Save" at the top and export your templates once you had updated these.
From The Builder:
Click "Template Footer"
then "Social Icons"
Then "Edit social links"