From the Title Details page, you can always change the default region settings for a single title.
Under the Settings section of the left of the page, select the orange arrow next to the "Region" section.
You'll now see these options:
To list on .co.uk, simply click the tick next to .co.uk. This would mean your title will appear on both NetGalley.co.uk and NetGalley.com.
You can also opt to receive requests only from certain regions. To do so, click the "Set Regions" text. This will allow you restrict requests from any of the UK, EU, Australia, US, or Canada.
This will not affect your default region settings for the account. Read more about your default settings.