Add in your .htaccess:
<IfModule mod_rewrite.c>
RewriteEngine on
RewriteCond %{HTTP_HOST} !^www\.
RewriteRule ^(.*)$ http://www.%{HTTP_HOST}/$1 [R=301,L]
</IfModule>
at the beginning of the file, before the # ~~start~~ row.
and set your domain name as www.gymrat.ru at BackOffice > Preferences > SEO & URLs
The opposite variant (WWW to NON-WWW) is the following:
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteCond %{HTTP_HOST} ^www\.(.*)$ [NC]
RewriteRule ^(.*)$ http://%1/$1 [R=301,L]
</IfModule>