Hello,

If you have added the medication to functions.php of the parent theme, all the changes would be lost. Move all your changes to the child theme. Make the full backup of your site. Recreate your header in the Header builder if you have not used Header builder.

Consider using this plugin https://wordpress.org/plugins/google-tag-manager/

All the CSS put in the parent. PHP should be put in the Child.

In any case, make the full backup of your site and try automatic update: Appearance > Themes > Woodmat > update https://xtemos.com/docs/woodmart/update-theme-2/

Best Regards