I have the same problem… I can't find any application in iOS to be able to connect it

Sad response from Razer, I understand not updating drivers, but removing the application you use to connect it... it only serves as a watch like an old Casio:

From Razer support: “With regards to your concern, we just want to set proper expectations that the Razer Nabu watch is a legacy device that can only be connected in the Nabu app and is not available in the App Store anymore.”

Same problem on Android,  and guess what: I JUST BOUGHT MY NABU X LAST WEEK!!! Obviously, they aren't calling back their product... So, I lost my money.

The only thing you can do it's downloading APK. I rather wait, hoping they won't let us down because the other way just way doesn't seems secure enough.