How do I unlock my iphone 8?

"Unlock" is very general. There's multiple kinds of locking on devices. Click on the links below to find instructions on how to deal with your specific situation:

1) iCloud: Activation Lock - http://support.apple.com/kb/PH13695 - This is a security feature so only legitimate (i.e., not stolen) redistribution of devices is possible. See: Turn off Find My iPhone Activation Lock - https://support.apple.com/HT201441 - If an activation lock was put on a device, only the owner of the account that applied the lock can remove it. Get them to remove it or return the item for a refund.

2) Device lock: "If you forgot the passcode for your iPhone, iPad, or iPod touch, or your device is disabled" click here --> https://support.apple.com/HT204306

3) Carrier lock: Read this link on "How to unlock your iPhone for use with a different carrier" - http://support.apple.com/HT201328 - Only some carriers offer the ability to unlock iPhone for use on any carrier. Follow the instructions in this article to unlock your iPhone.

i cant unlock my iphone8+ i dont remember the passcode