You start by reading the training materials, where you would've found out that in order to create iOS apps (even in Worklight, doesn't matter) - you need a Mac with XCode installed.
Developer Center: https://developer.ibm.com/mobilefirstplatform/documentation/getting-started-all-tutorials-6-3/
You need to open in XCode the XCode project that Worklight Studio generated for you. There you need to have it properly configured so that you could export an .ipa file (not related to Worklight - read Apple documentation). Once you have the .ipa file, you can upload it to the Application Center management console.