How To Redirect Pages In WordPress Without A Plugin
To redirect pages in WordPress without plugins, first copy the code of step 2 in the functions.php file, then change the "from" and "to" URLs to your desired URLs, and save the file.
Wordpress tutorials
Create child theme in WordPress step by step [without plugin]
To create a child theme, first find the "Text Domain" of your current theme in the stylesheet file. Then create the three files described in step two, zip them, and upload them to the site's themes section.