call custom action after delete account

It depends on what the function myAction() is doing.

Your order is this:

1. pluging defines action hook with do_action( 'bp_members_delete_account_after_submit' );

2. You hook a function on that with

   add_action( 'bp_members_delete_account_after_submit',
               'action_bp_members_delete_account_after_submit' );
   

3. the function action_bp_members_delete_account_after_submit() is then adding a hook named 'myAction' and passing it two arguments as strings 'arg1' and 'arg2'.

But there is nothing to “happen” in the code above, unless you have a function hooked to myAction.

add_action( 'myAction', 'my_function', 10, 2 );

function my_function( $first_arg, $second_arg ) {
     //here, $first_arg would be literally equal to text 'arg1'
     // $second_arg would be literally equal to the text 'arg2'

     //you would do stuff here
}

Of course, you could skip some of that and run the code you need run inside the action_bp_members_delete_account_after_submit() function by making it:

function action_bp_members_delete_account_after_submit() {
    //you would do stuff here, 
    //no need to make another hook if you are not going to hook things to it
}