come trasferire tutto lo storico presente nel dispositivo garmin al telefono nuovo ?

I bought a new phone with garmin connect installed. I have paired the phone with the device but I don't see the data history. How can I restore all old data of sleep heart rate etc etc.

You just have to use the same Garmin Connect account as on the old phone. That's all. If you do not see the old data on the new phone, then it means you created a new account instead of using the old one. Remove the watch from the new account (important!), remove the watch from the list of Bluetooth devices in Android system settings, sign out from Garmin Connect, then search your old credentials (email and password), log in back to your old account, and add the watch there.

son riuscito a trovare le attività precedenti ma per quanto riguarda i dati sulla frequenza cardiaca sonno stress etc etc mi partono da quando ho installato il dispositivo sul nuovo cellulare e non vedo quelli vecchi

I managed to find the previous activities but as regards the data on heart rate, sleep, stress etc etc, they start from when I installed the device on the new mobile phone and I don't see the old ones

As I wrote, you have to remove the watch from the new acount, sign out, then sign in with the old credentials, and add the new watch there.