How do I unlock an iPhone 11 from a previous owner?

There is another kind of lock: Activation Lock.

If the phone is Activation Locked to the Apple ID account of the person you bought it from, you will not be able to use the phone until that person helps you release the Activation Lock.

The phone should have been prepared as outlined in:

What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support

Regarding SIM Lock.......Until the former employee contacts the carrier to which the phone is locked and has them unlock it, the phone will be no more than a paperweight for your use.

Things would be much better if you could simply return the phone for a refund. Is that a possibility?

If not, assuming you can get a hold of the former employee, everything is on them to get the phone unlocked. Frankly, there is not much incentive for them to go to the extra trouble to do this, since they already have your money.

If the former employee was behind in their payments to the carrier, the phone has likely been "blacklisted", meaning that it cannot be used.

You will not be able to contact the carrier yourself, because you were not the carrier's customer.

There are 2 kinds of locks it could be and both will require the assistance of the cell provider that locked the device, but they are most likely not willing to help since you are not the account holder of the plan that locked the device.

• Carrier Lock - Will tie the phone to the carrier and not allow the device to be used on any other carrier. The previous owner is the only one that can remove this lock, since it will require information about the account and that will not be released to you for privacy reasons. It could be that the previous owner sill owed money on the device.
• SIM Lock - Users can set a PIN on the phone to prevent anyone else from being able to use the phone. If you do not know the SIM or forgot it, then you have to contact the cell provider to get that code. Again, the cell provider will only give this information to the person who had the account on their network and will not be able to give you any information.

You must take it to your SIM card carrier and they are able to unlock it

Grantlatto wrote:

You must take it to your SIM card carrier and they are able to unlock it

False. Only the carrier it is locked to can unlock it.

You must take it to your SIM card carrier and they are able to unlock it

This is not correct. The original carrier must unlock the phone.