You may follow the below steps to turn off the “connect automatically” option, for that hidden network.
1. Press Windows key + A to open action center and click on All Settings.
2. Now select Network and Internet.
3. In the left panel, select Wi-Fi.
4. Now in the right panel, select the option Change Adapter Options.
5. The Change Adapter Options will open the Network Connections. You will find the network connection to which your computer or tablet is connected.
6. Double click on the wireless connection to open the Wi-Fi status. Go to Wireless Properties.
7. Under Connection tab, find out “Connect automatically when this network is in range“. By default it is enabled. To disable it, uncheck the option and tap ok.
I hope that helps!