Delete users from WPLMS Site which logged in more than 3 months ago. Copy and past this code in Child theme - functions.php

delete_users.php

//Screenshot of how this works : http://prntscr.com/g1qkzf

add_action('in_admin_footer',function(){

	if(isset($_POST['delete_3_month_users']) && wp_verify_nonce($_POST['delete_3_month'],'delete_3_month') && current_user_can('manage_options')){
		global $wpdb;
		$results = $wpdb->get_results("SELECT user_id FROM {$wpdb->usermeta} WHERE `meta_key` = 'last_activity' and `meta_value` <= DATE_SUB(NOW(), INTERVAL 3 MONTH)"); // change interval to change duration.
		if(is_array($results)){
			echo '<div style="padding:15px;background:#fff;border:1px solid #eee;margin:15px 0;"><ol>';
			if(count($results)){foreach($results as $result){
				echo '<li>User Deleted : ID '.$result->user_id.'</li>';
				//wp_delete_user($result->user_id);
			}}else{
				echo '<li>No users found</li>';
			}
			echo '</ol></div>';
		}
	}
	echo '<form method="post">
		<input type="submit" name="delete_3_month_users" class="button-primary" value="Delete users 3 months old"/>
		';
		wp_nonce_field('delete_3_month','delete_3_month');
	echo '</form>';

},1);