I live in Ethiopia and how can I unlock my SIM card on my iPhone

If you can't activate your iPhone - Apple Support - "If your iPhone can't be activated or an alert says the activation server is unavailable or the SIM card is unsupported, learn what to do." Click here and read --> https://support.apple.com/HT201407

How to unlock your iPhone for use with a different carrier - http://support.apple.com/HT201328