Since OP is new to linux I’ll just add this in case it’s helpful.
To edit a file owned by root (super account) you can use sudoedit /etc/apt/sources.list or alternatively sudo nano /etc/apt/sources.list in a terminal.
In the editor save by using the key combo Ctrl+S and exit with Ctrl+X.
Commenting is adding a # in front of the line.
so the file should look like something like this
<pre style="background-color:#ffffff;">
<span style="color:#323232;"># deb cdrom:[Debian GNU/Linux 11.5.0 _Bullseye_ - Official amd64 NETINST 20220910-10:38]/ bullseye main
</span>