My iPhone 6 says sim card not supported

bebeth0103,

See this:

If you get an alert about the SIM card in your iPhone

Good luck.

Hi

Is your iPhone locked to another network provider,

Only they can remove the simlock.

Or you may have a faulty simcard reader.

Cheers

Brian 🇬-1F1E7;

When I try to put my SIM card from my other iPhone to my iPhone 6 it's say SIM card not supported

That's because the phone is carrier locked to a different carrier.