I am in Malawi am using iPhone 6 that was used in Hawaii but here in Malawi need to be sim card activated

You contact the carrier the phone is locked to. If you don't know who that is, call AppleCare and give them the serial number. They should be able to tell you. I would imagine it is locked to whatever carrier it was being used on in Hawaii.

If you're being told your SIM is unsupported, that means the phone is carrier locked. Only the carrier it is locked to can unlock it for use on other carriers. You will have to contact them.

You contact the carrier for that phone.