The following can be added to the .htaccess file to redirect all http request to https.

RewriteEngine On
RewriteCond %{HTTPS} off  
RewriteRule ^(.*)$ https://%{HTTP_HOST}%{REQUEST_URI} [R=301,L]

RewriteEngine On – Allows the rewrite capabilities. If it was off, the last rule “RewriteRule” would not work.
RewriteCond – This is a conditional that says if the current request is using HTTPS, don’t rewrite. If this option was not here, we would get an infinite redirect loop.
RewriteRule – This is the actual rule that rewrites or redirects any HTTP request to HTTPS. the R=301 means that it redirects using a 301 status code.

The following links provide more detail and info on htaccess redirects.

https://linuxize.com/post/htaccess-force-https/

https://www.redhat.com/sysadmin/beginners-guide-redirects-htaccess