Add these rules to the top of your root .htaccess file (above other rewrite rules) changing the two instances of domain.tld to your domain name.
RewriteEngine On
RewriteCond %{HTTPS} off
RewriteRule ^(.*)$ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]
RewriteCond %{HTTP_HOST} !^domain.tld$
RewriteRule (.*) https://domain.tld/$1 [R=301,L]
If your .htaccess file already has a RewriteEngine On line you can safely remove (or leave) the extra copies. You only need it once at the top above the RewriteCond %{HTTPS} off line.
Once uploaded to the root of the site it will force all visitors through the https/SSL secure version of the site.
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