Yes, you need to configure another port to use the UART. Let's take P8 as the uart_tx and P8 as uart_rx like you wanted. Make sure you assign these pins to the UART in the design wide resources.
Since the Kitprog acts as a USB-UART bridge, you need to have wires connected to the custom UART_TX and UART_RX pins if you aren't using the port 5 pins which are connected internally. The kit provides this option in the "PSoC5LP GPIO Expansion Header (J6)". You need to connect the pins 12 ---> 8 and P12 ---> 8 externally. Also, since J6 is not loaded, you need to populate the header here.
You can find more information on the schematics here: https://www.cypress.com/file/420846/download