See below, post #102 in this thread by Eterman

Sorry, not sure how as I do not have this particular router and I don't really understand your question.

i use dlink recovery mode to re-flash 2.08TM, since the usual interface only allows upgrade

i learned from this site : http://forums.dlink.com/index.php?topic=44909.0

preparation :
-download 2.08TM firmware on your computer
-connect your computer to router using LAN cable
-set your computer's ethernet ip to static ip 192.168.0.2

assess recovery mode :
-power off your router
-use a pin ( or something similar) and poke/press the reset button
-while hold-press the reset button for 3-5 seconds, press the power button while hold-press the reset button until you see the power indicator is in amber colour and blinking ( now router is in recovery mode )

re-flash 2.08TM firmware
-on your computer, open up browser and login to 192.168.0.1
-it will show Dlink Recovery mode
-click select to choose the 2.08TM firmware, and then click upload
-wait until the process finish, it will autorestart
-check the version, it should say 2.08TM 

setup unifi and wifi settings
-since the router is reset, all settings are lost
-you will need to re-enter all unifi settings and personal settings again.

It worked for me, i hoped it works for you 

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So nice, my router i reset also can't connect to internet   

you mean dns?