Since you forgot the password to Wi-Fi network, you need to reset the Linksys EA6900 to factory defaults. There are two (2) ways do this:
== Hardware Reset ==
Press and hold the Reset button on the back panel of the Linksys Smart Wi-Fi Router for about 10 seconds then release.
== Software Reset ==
Log in to your Linksys Smart Wi-Fi Account. Under Router Settings, click Troubleshooting > Diagnostics. Click Reset under Factory reset.