Yes, the datasheet says everything you need to know about how to auth and change the chip… but it’s dry as hell. I’ve stated the problem elsewhere on the forum but basically the apps available do not just use the password you type… they transform the data somehow… so in the Dangerous NFC app for example, when you set a password for the xNT, if you type NExT then the password block will be set to 0x4E 0x45 0x78 0x54 however if you use TagWriter to set the password, type NExT, then the password block is not set to 0x4E 0x45 0x78 0x54 it’s set to something else… same with NFC Tools. I have no idea why they do this… it’s down right dumb… but the end result is that if you want to use either of those tools to change the password, they will ask you to type it… and if you type NExT then those apps will try to auth with something that isn’t 0x4E 0x45 0x78 0x54… so you get a failure. I don’t know why software developers do this… it only hurts you.
There are a few threads on the forum where I mention the use of NFC Shell, which is a great app that lets you chain together raw commands and send them to the tag. NFC Tools has a similar feature in the advanced section, but critically you can only send one command at a time, which is virtually useless when dealing with authentication processes, which always require an auth command before any changes to protected areas can be changed.
https://forum.dangerousthings.com/search?q=nfc%20shell
If you use NFC Shell you can auth with 0x4E 0x45 0x78 0x54 then write FF FF FF FF to the password block… which is the factory default… then you can use NFC Tools or TagWriter to make whatever changes you want and set the password or whatever…
My primary question though is - why do you want to change or remove the password on your NExT… by default it does nothing but protect the configuration pages from accidental or malicious changes.