How do I integrate the watchos app into a live IOS app?

When you add a Watch app target to your existing iOS project, you're creating a separate app with a special relationship to the iOS app. (It's not embedded in the iOS app, but it is partnered—and submitted to the App Store—with it.) Your Watch app needs its own bundleID, and it must have the same root as the iOS app's bundleID (e.g., if com.mycompany.myapp is the iOS app's bundleID, com.mycompany.myapp.watchkitapp would be the watchOS app's bundleID). This bundleID must be registered to your developer account and have its own associated provisioning profile. Do you have automatic provisioning set up, such that Xcode can register the watchOS app's bundleID and create a provisioning profile for you? If not, you will need to do these steps manually.

Is there a chance you had a watch app before and this bundleID is already registered to your account, or that this bundleID was registered to a different account than you're attempting to sign the app with now?

Firstly, thanks for your response. The bundle id of the ios application is added in the applestore, but a bundle id with .watchbookp extension is not added. When I try to add manually, I get an error like this :

Where is that error being presented? In Xcode or App Store Connect?

I am getting error from App Store Connect when trying to create AppID as com.servislet.ServisletV2.watchkitapp. When I try to install without creating an AppID, Xcode gives an error: Failed to register bundle identifier.