User Profile

Hello everyone,I've been developing an Interval Training App for iOS using SWIFT using a Timer Object. Everything is working perfectly with the App except when it goes on the background. For example, if a user exist the app to go to another app (for example a music app) the Timer stops and everything stops on the App. Does anyone know how to deal with this situation? I've seen many apps similar to mine working perfectly when they go on the background (for example "IntervalTimer" ou "HIIT & Tabata").Thanks in advance.