iphone 15 as gift

I received an iphone 15 as a gift, bought from a t-mobile store I think.  I just switched to t-mobile and got new phones.  How can switch my current phone out to the iphone 15 and give my husband my current phone?  He has an android phone with a t-mobile sim.  My current t-mobile phone is a Pixel 8 with an esim.  Do I need to contact t-mobile to do this?