How do I unlock a disabled iPhone 6 without itunes?

If the iPhone is disabled because the passcode has been lost, the iPhone needs to be restored.

If you setup your iPhone security such that it will auto-erase after 10 failed passcode attempts, you could keep entering passcodes until the iPhone erases itself.

If you didn't setup that security option, here is another option. If your Apple ID is still logged into the iPhone and the iPhone has an active internet connection, log into https://www.icloud.com/#find and erase the iPhone. You would then be able to restore from an iCloud backup (if you have one) or setup the iPhone as new.

If erasing the iPhone via iClould is not an option, you will need iTunes. Since you are asking for a solution without iTunes, I won't go into that solution; however, here is a link that gives you that detail. https://support.apple.com/en-us/HT201263

Without iTunes, I would recommend bringing the iPhone to an Apple Store where they would be able to restore the iPhone for you.

Good luck!