.htaccess dosyası kesin olarak yok diyorsan ftp bağlanıp ".htaccess" adında dosya oluştur ve aşağıdaki kodu ekle ardından gerekli SSL ayar kodlarını ekle ondan sonra tamamdır.
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php[L]
</IfModule>

Kolay gelsin, HTTPS için, siteadresi.com/admin.php giriş yapın ardından forum ayarlarınızdan url adresinizin başına HTTPS yazın kendisi yönlendir, htaccess için ise kodu aşağıya bıraktım.

#    Mod_security can interfere with uploading of content such as attachments. If you
#    cannot attach files, remove the "#" from the lines below.
<IfModule mod_security.c>
    SecFilterEngine Off
    SecFilterScanPOST Off
</IfModule>

ErrorDocument 401 default
ErrorDocument 403 default
ErrorDocument 404 default
ErrorDocument 405 default
ErrorDocument 406 default
ErrorDocument 500 default
ErrorDocument 501 default
ErrorDocument 503 default

<IfModule mod_rewrite.c>
    RewriteEngine On

    #    If you are having problems with the rewrite rules, remove the "#" from the
    #    line that begins "RewriteBase" below. You will also have to change the path
    #    of the rewrite to reflect the path to your XenForo installation.
    #RewriteBase /xenforo

    #    This line may be needed to workaround HTTP Basic auth issues when using PHP as a CGI.
    #RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]

    RewriteCond %{REQUEST_FILENAME} -f [OR]
    RewriteCond %{REQUEST_FILENAME} -l [OR]
    RewriteCond %{REQUEST_FILENAME} -d
    RewriteRule ^.*$ - [NC,L]
    RewriteRule ^(data/|js/|styles/|install/|favicon\.ico|crossdomain\.xml|robots\.txt) - [NC,L]
    RewriteRule ^.*$ index.php [NC,L]
</IfModule>
# php -- BEGIN cPanel-generated handler, do not edit
# “ea-php74” paketini varsayılan “PHP” programlama dili olarak ayarlayın.
<IfModule mime_module>
  AddHandler application/x-httpd-ea-php74 .php .php7 .phtml
</IfModule>
# php -- END cPanel-generated handler, do not edit

.htaccess dosyasını publichtml dizinine oluşturup, aşağıdaki kodları yapıştırıp kaydededersen sorun kalkmış olacak;

RewriteEngine On RewriteCond %{SERVER_PORT} 80 RewriteRule ^.*$ https://%{SERVER_NAME}%{REQUEST_URI} [R=301,L]

Sunucunuza FTP üzerinden bağlantı kurun .htaccess dosyası yok ise aşağıdaki gibi oluşturun. Aşağıdaki kod hem xenforo varsayılanı + hem de ssl için gerekli yönlendirmeye sahiptir

#    Mod_security can interfere with uploading of content such as attachments. If you
#    cannot attach files, remove the "#" from the lines below.
#<IfModule mod_security.c>
#    SecFilterEngine Off
#    SecFilterScanPOST Off
#</IfModule>

ErrorDocument 401 default
ErrorDocument 403 default
ErrorDocument 404 default
ErrorDocument 405 default
ErrorDocument 406 default
ErrorDocument 500 default
ErrorDocument 501 default
ErrorDocument 503 default

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

    #    If you are having problems with the rewrite rules, remove the "#" from the
    #    line that begins "RewriteBase" below. You will also have to change the path
    #    of the rewrite to reflect the path to your XenForo installation.
    #RewriteBase /xenforo

    #    This line may be needed to workaround HTTP Basic auth issues when using PHP as a CGI.
    #RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]

    RewriteCond %{REQUEST_FILENAME} -f [OR]
    RewriteCond %{REQUEST_FILENAME} -l [OR]
    RewriteCond %{REQUEST_FILENAME} -d
    RewriteRule ^.*$ - [NC,L]
    RewriteRule ^(data/|js/|styles/|install/|favicon\.ico|crossdomain\.xml|robots\.txt) - [NC,L]
    RewriteRule ^.*$ index.php [NC,L]
</IfModule>