website with www prefix does not load

I’ve tried to install this plugin and got several errors so I uninstalled it. Since then when I try to accesss my website using www prefix it tries to download a file with the following text:
“<b>Warning</b>: Cannot modify header information – headers already sent by (output started at /home/my-site/public_html/wp-content/plugins/above-the-fold-optimization/includes/abovethefold.class.php:95) in <b>/home/my-site/public_html/wp-includes/pluggable.php</b> on line <b>1207</b>
“

How can i fix it?
my website is viagemempauta.com.br (and the problem occurs when I try to access through https://www.viagemempauta.com.br)

https://www.ads-software.com/plugins/above-the-fold-optimization/