You don’t “add drones”.
Sorry. 
you list your drones.
Making sure the policy will cover all drone specified.
The GADC Insurance does not ask for any drone information.
Edit: Ahh … following back many post, you refer to Coverdrone.
I also use Grey Arrow PLI and Coverdrone to, um, cover the drone. My drone was a total loss on Tuesday evening after a seagull attack (it was tipped, lost control, and fell into the sea, irrecoverably in a dredged deepwater shipping channel). As it happened, I’d taken out the Coverdrone policy the previous Thursday, a good decision in the event. The drone will have to be replaced, and unless DJI can supply the drone only with no controller that will be £199 (£249 less the £50 excess) for a spend of £2.14 monthly, as good a £2.14 as I’ve ever spent! You can follow my progress over on General Drone Discussion under the heading ‘RIP Mr.Drone, lost at sea’. The claim went in on Friday evening and should (x fingers) be straightforward enough, but I will report progress on that topic.
Speaking to Coverdrone on the phone last week I found them most helpful, a good sign.
Did you not consider care refresh ?