Can't get Comments Control to work

I'm struggling to get Comments Control to work.

The instructions are very straight forward:

1. Go to Settings > Network Settings in the network admin dashboard.

2. Scroll down to the Comment section, configure the IP addresses as desired.

3. Click Save Changes

However, when I go to Settings, there is no sub tab for "Network Settings".

There is a sub tab called "Comment Control" but that does not have any box to be able to configure the IP addresses.

I don't understand what's going on here. Can someone help please?

Thanks.

Alastair