how to set up airport time capsule as external hard disk

The Time Capsule will need to connect to your router using a permanent, wired Ethernet cable connection. You can locate the Time Capsule anywhere that the Ethernet cable will reach, up to about 100 meters or 325 feet from your main router.

Perform a Hard Reset on the Time Capsule and then use the AirPort Utility setup "wizard" to configure the Time Capsule again. The wizard will set up the Time Capsule to provide a WiFi network, but you can turn off the WiFi function later if you wish and use the Time Capsule only as a wired hard drive.

If you need step-by-step instructions, we'll first need to know........

1) The make and model number of your modem/router or router

2) Whether you plan to set up the Time Capsule using a Mac or a PC

3) Whether you will be using the Time Capsule to back up your Mac(s) using Time Machine

Setting up the 2TB Time Capsule as a NAS.… - Apple Community

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https://www.google.com/search?q=use+time+capsule+as+nas&oq=use+time&aqs=chrome.1.69i57j0l6.5553j0j7&sourceid=chrome&ie=UTF-8

A Hard Reset will not wipe or erase the data on the Time Capsule hard drive, so hopefully you will not forget to also manually and securely erase the data on the Time Capsule hard drive......unless you plan to provide the next owner with a lot of your personal data.