Options using non-T-Mobile modems for home internet

I just joined T-Mobile using the 5G internet and we moved two cell phones over as well.  With all my previous ISP's I had the ability to "manage" my own intranet.  I was able to setup the DHCP pool and be able to assign static IP addresses outside the range of the assigned pool, eliminating addressing conflicts.  With this new "white" router, I cannot see or change any network settings on my side of the router.  If ANYONE knows how to do this please share your knowledge.