AX1800 bought used. Need to retrieve password.

What router?

AX1800 is not a unique Netgear model number. Many devices come with the AC/AX tag, but it is essentially a label that Netgear, and others, attach to hardware to describe wifi speeds.

Look at the label on the device for the Model Number. And, if there is one, include the "V" bit to show the hardware version. If there is no V number, then you have V1.

Manuals are always a good place to start.

Visit the support pages:

Support | NETGEAR

Feed in your model number and check the documentation for your hardware.

Look for the model number on the label on the device.

That page will also have any software, firmware and drivers for your device, if they exist.

Look for details on how to reset the router.

There is nothing to be gained by recovering old settings. Your Internet service won't be the same.