There's currently no option to change the link from this menu. However, please try adding the following Javascript code to your theme files. 

Please follow the steps below:

    1. Go to BuddyBoss - Theme Options.

    2. Under Custom Codes, enable JavaScript.

    3. Append the following:

jQuery(document).ready(function() {

jQuery("#activity-following").addClass("selected");

jQuery("#activity-all").removeClass("selected");

jQuery("#activity-following .bb-component-nav-item-point").click();

});

    4. Click Save Changes. 

Note: Any modifications are considered as custom work already. Know more about our Support policy here: https://www.buddyboss.com/support-policy/

Screenshot: