how do i get it back? I am the developer of it and for several years it was on the App Store I is my copy and has vast amount of information in it that i value

I've created a simple count down timer app in Swift. It works great except when i minimize the app, the timer stops ( and starts again immediatly again when i bring the app back up). I want the timer to continue ( even if minimized) and execute an action. Does anyone have a suggestion??Thank you..