Hello @kkjdroid. I'm not sure I understood you correctly. Still, I made some changes, try it.

<?php
/*
Plugin Name: BuddyPress Group Test
Plugin URI: n/a
Description: Test adding group tab
Version: 0.0.1
Author: n/a
Author URI: n/a
License: AGPLv3
*/

add_action('bp_actions', function() {
    if (bp_is_group()) {
        $group = groups_get_current_group();
        if ($group) {
            $group_slug = $group->slug;
            bp_core_remove_subnav_item($group_slug . '_manage', 'group-avatar', 'groups');
        }
    } else {
        bp_core_remove_subnav_item('profile', 'change-avatar', 'members');
    }
});

add_action('bp_setup_nav', function() {
    $bp = buddypress();
    if (bp_is_group()) {
        $group = groups_get_current_group();
        if ($group) {
            $group_slug = $group->slug;
            $parent_url = trailingslashit(bp_get_group_permalink($group)) . 'admin/';
            bp_core_new_subnav_item([
                'name' => 'Change Group Photo',
                'slug' => 'change-group-photo',
                'parent_url' => $parent_url,
                'parent_slug' => $group_slug . '_manage',
                'position' => 30,
                'screen_function' => function() {
                    bp_core_load_template(apply_filters('bp_core_template_plugin', 'groups/single/plugins'));
                    add_action('bp_template_content', function() {
                        echo '<h1>GROUP</h1>';
                    });
                },
            ]);
        }
    } else {
        if (is_user_logged_in()) {
            $user = wp_get_current_user();
            $parent_url = trailingslashit($bp->loggedin_user->domain . $bp->profile->slug);
            bp_core_new_subnav_item([
                'name' => 'Change Profile Photo',
                'slug' => 'change-profile-photo',
                'parent_url' => $parent_url,
                'parent_slug' => $bp->profile->slug,
                'position' => 30,
                'screen_function' => function() {
                    bp_core_load_template(apply_filters('bp_core_template_plugin', 'members/single/plugins'));
                    add_action('bp_template_content', function() {
                        echo '<h1>USER</h1>';
                    });
                },
            ]);
        }
    }
}, 10);
?>