How can I make my iPhone 7 model A1778 CDMA compatible?

Thank you. When I bought my cell iPhone from the Apple store I stressed I wanted a network compatible CDMA and GSM cell phone. My bad for not double checking and taking Apple associate word for granted. Buyers beware as it is said.

I see that iPhone 7 model A1660 works both CDMA and GSM while A1778 only does for GSM. Guess I was and easy target to be sold A1778 model rather than the A1660 when asking Apple associate for a compatible model for both networks. It is really upsetting being taken advantage of for lack of knowledge. Apple associate lacked honesty when selling the phone to me.

When I bought the phone I told the Apple associate that I was looking to use it with any carrier and both within the US and overseas. At that time I was not aware of the networks difference (GSM vs CDMA) which I do know.

I was using T-Mobile and was looking to move to Tello but the later does not support GSM but CDMA. I am looking now for another carrier that supports GSM with similar prices as Tello, Red Pocket supports such network and am checking its reviews before making the move.

I did not buy an iPhone to work specifically with Verizon and/or Sprint but wanted it to work with all 4 major US carriers which is not the case (only GSM). I will stick to only GSM carriers as I cannot buy an iPhone every other week/month/year each time I change to other carrier with a different network. CDMA carriers like Tello are out of the question.