Making an existing consultation private is nice and simple, but your consultation must be retracted in order to make the change.
1. From the consultation dashboard select 'Retract' and then 'Edit Consultation Details'.
2. Scroll down to the 'Private consultation' section and tick 'Make this consultation private'.
3. Then select 'Save' (bottom right of the page).
4. Go back to the Consultation Dashboard and select 'Publish'.
How the URL will change
Once a consultation is made private, the pathname will change from the text you had originally assigned to it to an alpha-numeric code, like this:
If your consultation is currently open (i.e. today's date is within the start and end dates you have put in your 'Edit consultation details' section) then you'll be prevented from making your consultation private. The reasons why are listed in this article about it.
To make the change in this case, you'll need to temporarily update your start date so that it is after today's date, save, and then select the 'make this consultation private' checkbox. You can then reset the start date to its original date, save and republish. BE AWARE: Your consultation URL will change if you toggle your consultation from public to private and vice versa, so if you have respondents in the middle of completing it then they may lose their response. Be mindful of this when making any change and only do so if you are happy you won't be interrupting anyone's response.