Hi @Mish08 when changing phones, there is no need to setup the Sense or pair the tracker to the phone.
Is the Sense still connected to your Fitbit account?
First step, if the old phone is nearby and turned on, log out of the fitbit app and remove the sense from the Bluetooth menu.
On the new phone.
That is all, the Fitbit app will pair the Sense and the tracker should sync.
Now if the tracker was removed from your Fitbit account, we will need to setup the tracker as if it was purchased today.