I need a WPA2 password for a MyOptimum network

Did you just recently receive an Optimum router for use in your home. On initial install, the network name and password should be on a sticker attached to the router.

Beyond that you would create the Password on the router when you set up a network that is different than the default network provided. How you do that depends on which specific model of router you have. Your Mac will save the WiFi password the first time you enter it to log into the network, but it cannot find the password on the router when you have not previously entered it.

Optimum apparently uses a password sticker on at least some of their Wi-Fi routers:

https://www.optimum.net/cdn/static.tvlistings.optimum.net/ool/static/prod/documents/user-guides/SC_Apr_GUI_SagemcomModemGuide_COL0416SAGE33913_WEB_ENG.pdf