apache module (ADD WWW) not works

I’ve tried to enable the feature “Add WWW” in the options to redirect any https://website.ext to https//www.website.ext but the code added to the end of .htaccess is empty:

# Created by Redirection
# Tue, 17 Oct 2017 10:48:27 +0000
# Redirection 2.7.3 – http://urbangiraffe.com/plugins/redirection/

<IfModule mod_rewrite.c>
</IfModule>

# End of Redirection