Hello again @Launig
I think I fully understand now. Your husband got a new Fitbit. You now have his old Flex 2 and your trying to add his Flex 2 to your existing account. (Hopefully I have this correct) First make sure that your husband no longer has his old Flex 2 connected to his Bluetooth. It can cause conflicts. If “you” previously had a Fitbit that was paired to your iPhone 6 make sure you remove your old one as well from your phone since your adding his old Flex 2 to your existing account.
Once you have done all that please go to the Bluetooth settings on your phone and remove the tracker. In the list of Bluetooth devices you'll see the Fitbit Tracker and next to it, this symbol "!". Hit the symbol and it will take you to the next step, once you're there select the option that says "Forget this device" or "Unpair". Once you've made sure about that, go back to the Fitbit app, tap your profile picture then scroll down and select "Set up a Device". This should start the setup process for your device. Just follow the instructions as they come.
If the issue is not solved after the above steps, please take a look at the help articles: Why can't I set up my Fitbit device? or Why won't my Fitbit device sync?
😃please let me know how it goes
