That WIKI is to set up as a router so you just need to set up the ATM connection screen and the layer2 interface on the WAN connection screen to use the ATM name.
Leave the modem in bridge mode which it is by default, there will be no Username details and password in the modem, that is done in the Google Wifi.
Also on the DSL configuration screen you will probably want ADSL2+ ticked. It may be set to all types already. It also is a good idea to disable the QOS function as it can reduce the upstream speed, although on ADSL it may not have much effect.
Hope this helps.