Detailed below is the instructions from ASUS on how to put the DSL-AC88U into Recovery Mode (Rescue Mode) to enable the loading of firmware from outside of the Routers UI (User Interface) and also details (simple) on how to clear the DSL-AC88U NVRAM.
(Also works for DSL-AC3100 and DSL-AC88U Annex B)
Put the DSL-AC88U into recovery mode (it should be the “rescue mode”):
[On your Router]
- First, unplug the power core (DC IN) of DSL-AC88U Router.
Next, long-press the button “RESTORE” about 5 seconds and plug in DC IN behind the DSL-AC88U Router.
The DSL-AC88U router is on rescue mode now (no LED’s blink but WiFi LEDS Glow Dull).
[On your Computer]
Connect with computer and DSL-AC88U Router as bellow picture – green line(LAN).

Click 「Start」→「Control panel」→ 「network and Internet」→「Network and Sharing Center」→「Change adapter settings」at left page

「LAN」→right click「properties」→click「Internet protocol version 4 (TCP/IPv4)」→click 「properties」at the bottom of page→modify the content as bellow

Use the following IP address,IP address:192.168.1.10, subnet mask:255.255.255.0 → click「OK」
You can update the firmware by entering the URL “192.168.1.1” via your browser:

If the update is successful, a message will appear stating the update will take about 2 minutes

2) How to erase the routers NVRAM?
Go to the Administration > Restore/Save/Upload Setting page, and press the “Restore” button of the “Factory Default” option.
Hope this Proves Usefull?
UK Sentinel