increase max_input_vars value and htaccess

hi, for a theme i use i have to increase max_input_vars value to 2000
my hosting provider told me to do this in my .htaccess with a line:
php_flag max_input_vars 2000

my .htaccess file is like this:

# BEGIN WordPress

RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]

# add a trailing slash to /wp-admin
RewriteRule ^([_0-9a-zA-Z-]+/)?wp-admin$ $1wp-admin/ [R=301,L]

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ - [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(wp-(content|admin|includes).*) $2 [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(.*\.php)$ $2 [L]
RewriteRule . index.php [L]

php_flag max_input_vars 2000 

# END WordPress

when i insert the line i become a error:

Input variables exceeded 0. To increase the limit change max_input_vars in php.ini. in /home/httpd/vhosts/xxxxxxx.de/httpdocs/wp-includes/formatting.php on line 3319

can somebody please help me with this, i do hav no knowledge about this, i have a wp multisite, can i delete the whole .htaccess file and insert only the line php_flag max_input_vars 2000 ?