You have two options,

#1
1. Clone your WebApp and create a new one with a new URL. 
2. In your Site group settings, create a new one and set the URL of the new web app and keep the older one as it is. 

Run it. Now you have 2 CD instances and 1 CM instance. 

#2
If you are using any standard or above plan like S1, S2, S3.. (I believe you have as you are asking for the production environment) then you can create a slot and copy all the content over there. Use the URL of your slot and create a new option in Site group settings and access it. 

#1 should be recommended. The only advantage of Slots is, you don't need to pay any extra cost. 

Please note, for both approaches, you have to deploy the code base separately. 


Usually, we upscale the UAT environment like the production and do the testing over there. You can also go for that route instead of creating a new instance if it is suitable for you.