2.4 and 5 both working

[caperrymath]

If my extender is already setup, how do I go back setup for both 2.4 and 5?

[plemans]

Page 22 of the manual walks you through it. 

https://www.downloads.netgear.com/files/GDC/EX3700/EX3700_UM_8may2015.pdf

To change the WiFi network name:
1. On a computer or WiFi device that is connected to the extender network, launch a web
browser.
2. In the address field of your browser, enter the www-mywifiext-net    it doesn't let me type the actual address. 
3. When prompted, enter your email address and password.
4. Click the Menu icon .
The extender menu displays.
5. Select Settings > WiFi.
6. In each Network Name (SSID) field, type a network name.
7. Click the SAVE button.
Your settings are saved.

Here's the support site with your device with more troubleshooting, firmware and faq

https://www.netgear.com/support/product/EX3700.aspx