Finally had some time to move my TTN gateway from V2 to V2 network. Here are the steps and screenshots.

Prerequisites:
- Running v1.08 gateway firmware (beta)
- User account for TTN console (Community Edition)

Visit https://www.thethingsindustries.com/docs/download/ for the options

  1. Create a gateway in V3.
    a. Visit https://eu1.cloud.thethings.network/console/gateways/add if you live in Europe.
    b. Give the gateway a name. (Gateway ID)
    c. Choose the frequency plan 'Europe 863-870 MHz (SF9 for RX2 - recommended)' I'm a Dutch guy.
    d. Save
  2. Goto V3 gateway API Settings
    a. Select Add API key
    b. Provide a name
    c. Select 'Grant Individual Rights'
    d. Choose 'Link as Gateway to a Gateway Server for traffic exchange, i.e. write uplink and read downlink
    e. Generate API key
    f.  Copy key to clipboard and store safely, you can only look at it now.
    g. Click 'I have copied the key'
  3. Now we need to enter the new settings inside of the gateway
    a. Power cycle gateway with holding the pink reset button inside for 5 seconds.
    b. Browse to it's local website to fill in the gateway settings (I use wired LAN, so I skip the WLAN part)
    c. In Account server field replace https://account.thethingsnetwork.org with the URL from V3 https://eu1.cloud.thethings.network/
    d. At Gateway Key fill in the API key from 2f.
    e. Save

After creation the new gateway show 'Disconnected':

Filling in the new settings:

The gateway will now restart and connect to the new V3 enviroment:

A few moments later you will see it online, if all goes well:

Success!