Start util wpa_cli and execute commands:

> add_network

0

> set_network 0 ssid "MyNetworkSSID"

OK

> set_network 0 psk "MyNetworkPassword"

OK

> enable_network 0

OK

> save_config

OK

> quit

You can add multiple networks in a similar way. They will have different IDs, and the device will connect to any of them automatically.