@Smayl,

If you are looking to have both your Optimum Wi-Fi and your Decos broadcasting (not necessarily recommended for full mesh functionality), you would need to first configure the Decos normally, and then change their operation mode to AP Mode.

See these FAQs:

How to setup Deco with another Router

Difference Between AP Mode and Router Mode on Deco

Ideally, you would want to place your Optimum Router / Gateway in 'IP Passthrough' or 'Bridge Mode' (turning the Optimum Gateway into a simple modem); this would allow you to use the Decos in their default mode, will removed the Optimum Wi-Fi, and will make your Decos in charge of managing the security and routing of your network. If they were in AP mode, many of the responsibilities of the network would still occur and be run by the ISP Wi-Fi / Router