can't connect with 4g

hello guys, i have LG G2 VS980 for Verizon in settings i find that it works with 4g, but isn't work with 4g. previously i had the same phone with same problem, but a technical was solve the problem by using rom of t-mobile rather of verizon rom and it works, so how i can do it by myself, i have some experience of installing samsung roms.