Apple Watch ECG not working

Since past 2 months my Apple Watch 6 cellular ECG app is not working on putting my finger on the dial. Once in a while after repeated attempts it starts working but stops in between. But I am able to take my heat rate by applying finger on the dial separately and also on putting it on wrist. Seems like a software issue. Tried all setting reset in my watch and iPhone XR but still no result. What to do.