Unable to customize themes in wordpress after migrating to https from http

Run bellow query in your MySQL:

UPDATE wp_options SET option_value = replace(option_value, 'http://', 'https://') WHERE option_name="home" OR option_name="siteurl";
UPDATE wp_posts SET guid = replace(guid, 'http://','https://');
UPDATE wp_posts SET post_content = replace(post_content, 'http://', 'https://');
UPDATE wp_postmeta SET meta_value = replace(meta_value,'http://','https://');

Or you can Add the following code above the “That’s all, stop editing!” line in your wp-config.php file define('FORCE_SSL_ADMIN', true);