Retaining the Router Function of My Orbi Mesh Network with the T-Mobile Home Internet 5G Gateway

I have the same question.  I had added (actually Best Buy) an orbi mesh network with satellites to my at&t fiber router.  Now I am changing to t-mobil home internet.  When I signed up for this I was told by the t-mobil rep moving my orbi system to the new gateway would be no problem.  Well, I called Into t-mobil asking for help to do this - only after putting the t-mobil gateway in place was I informed by the tech that he could not help me with the orbi mesh hook up.  So now do I have to pay for another tech to come to the house to set this up? or is there anyone at t-mobil who can help me do this.  I am a computer appreciator not a comp expert!