How do you track your cycle on the app with no period?

So I’ve been on the IUD for 2 years now and I don’t have a period anymore. I get some cycle systems like discharge, breast pain, acne, etc, but I never have a period itself. I find it so hard to track my cycle with this app but I wonder how other people do it. I like being able to track where I am in my cycle because I’m sexually active but not in a committed relationship, and i just like the peace of mind. So how do you track it when the app ask if your period has started and you don’t know ?