Add custom settings page

wp-crm-system.php

<?php
// Add a tab to the dashboard page
function wpcrm_system_custom_setting_tab() {
  //Get current dashboard tab name
	global $wpcrm_active_tab; 
	//Be sure that 'my-tab-name' is the same in both places! ?>
	<a class="nav-tab <?php echo $wpcrm_active_tab == 'my-tab-name' ? 'nav-tab-active' : ''; ?>" href="?page=wpcrm-settings&tab=my-tab-name"><?php _e('My Tab Name', 'wp-crm-system') ?></a>
<?php }
add_action( 'wpcrm_system_settings_tab', 'wpcrm_system_custom_setting_tab' );

function wpcrm_custom_settings_content() {
  //Get current dashboard tab name
	global $wpcrm_active_tab;
	if ($wpcrm_active_tab == 'my-tab-name') {
		// include your plugin's settings content here
	}
}
add_action( 'wpcrm_system_settings_content', 'wpcrm_custom_settings_content' );