To redirect site http to https in wordpress, the most easy way is to use wordpres plugin.
Force WordPress Redirect Http to Https with Easy HTTPS (SSL) Redirection
However, if you do not want to use wordpress plugin, you also can use .htaccess to redirect http to https.
If you do not know how to open and edit wordpress .htaccess, you can refer this article.
An Easy Way to Edit WordPress .htaccess with Yoast SEO Plugin
In this article, we instroduce some examples to redirect http to https with .htaccess.
Example 1. Redirect All site HTTP URLs to HTTPS
Add the following code to your .htaccess file
RewriteEngine On RewriteCond %{SERVER_PORT} 80 RewriteRule ^(.*)$ https://www.yourdomain.com/$1 [R,L]
Example 2. Redirect Only a Specific HTTP Domain to HTTPS
RewriteEngine On
RewriteCond %{HTTP_HOST} ^yourdomain\.com [NC]
RewriteCond %{SERVER_PORT} 80
RewriteRule ^(.*)$ https://www.yourdomain.com/$1 [R,L]
Example 3. Redirect Only a Specific Folder
RewriteEngine On RewriteCond %{SERVER_PORT} 80 RewriteCond %{REQUEST_URI} folder RewriteRule ^(.*)$ https://www.yourdomain.com/folder/$1 [R,L]
Note: Replace “yourdomain” with your actual domain name wherever required. Also, as to folder, replace /folder with the actual folder name.