override function from my plugin [closed]

In WordPress ‘do_action’ is used to add an action hook in a plugin, which then can be used to hook our own function with plugin.

Check Codex for more details: Hooks API WordPress

To add your own function you will have to do the following:

add_action('groups_screen_group_request_membership', 'your_function_callback');

function your_function_callback($id){

    //here id can be used to get the id of current group
   //write your code here

}

Feel free to ask if you have any doubts.