We have not done a B2B since prior to the pandemic, but I understand the procedures are still pretty similar. You will get a notice in your cabin before the end of the first cruise that will outline the procedure. When we did it, all the B2B passengers met at a certain location, we were led off the ship, went through customs and then went right back on the ship before any of the new passengers. We had the same cabin for both legs although it is not abnormal to have different cabins, it just depends on how it was booked. From what I understand, you will pack up your things and your room steward should be able to assist you in getting things moved to the new cabin. There is definitely no need to take your belongings off the ship during the turn around.