Are you a T-Mobile USA customer?  Does your device and account meet all of the SIM Unlock Policy requirements?  

SIM Unlock Policy | Unlock Your Mobile Wireless Device | T-Mobile

i am not T-Mobile USA customer. I got the phone from a third party. I want to use it in Botswana, Africa.

Unfortunately, you do not meet the SIM Unlock Policy requirements.  You must be a T-Mobile USA customer and all of the SIM Unlock conditions must be met.  If you purchased it through something like Ebay.  See if you can return it for a refund.

noted. thanks for helping.

i want to unlock my iphone 11 pro carrier 

this one locked by usa sprint can you help me 

model - iphone 11 pro

imei - 35 323310 406645 1

Are you a T-Mobile USA customer?  Does your account and device meet all of the SIM Unlock Policy requirements mentioned earlier in this thread?  If so, then follow the instructions at the link marked as the answer and follow the instructions.  If not.  Then there is nothing T-Mobile can do to SIM unlock your device and you should return it to the place or seller you purchased it from.

yes i fulfil your requirements i want to use this phone in united arab emirates please help me

Follow the instructions to verify your T-Mobile account with Customer Care or the T-Force Team so they can verify you meet the requirements so they can SIM unlock the device, but only once you have verified to them that you and your T-Mobile USA account meet all of the requirements.

https://www.t-mobile.com/responsibility/consumer-info/policies/sim-unlock-policy