Important: This website is now read only (except to admins) to comply with the UK Online Safety Act. Composr CMS is in the process of migrating to a new Constitutional governance model and Bazaar development model, with functionality of the old website (constructed by ocProducts Ltd, the prior copyright holder, a UK company) spread between GitLab and the new website (which has no connections to the UK).
You could just make a copy of themes/default/GLOBAL_HTML_WRAP.tpl and move it to the custom_templates/ directory and hardcore the social media links into an appropriate area of that template, Probably the easiest way to do it as there is no addon or block for this currently.