Inxide sx 08 Spinning bike ,cardio e apple

Hello everyone,
I have a spin bike and I’m trying to find the best way to lose weight and train my legs. I love spinning!
I’m a bit confused because I need to track my heart rate with my heart rate monitor. I have an iPhone, a smartwatch, and a Polar heart rate monitor.

Is it correct if I connect the heart rate monitor to my smartwatch? The problem is that in this way it won’t be connected to the bike. So I think it might be better to connect the bike directly to the heart rate monitor.

How can I do that? Can it be done through an app?

Thank you!