The PmodAD2 communicates over I2C protocol with the main board on which the Pmod is plugged. The PmodAD2 has no UART / USB capabilities.
It is the main board that communicates - using its USB-UART capability - with the PC. Connecting the board using a USB cable creates a COM port on the PC. When you open a TeraTerm (or other terminal) connection, you select the COM port.
Therefore a possible approach could be to have 2 PmodAD2 connected to a single main board, in different Pmod connectors. The SDK application should gather the AD2 data (measurements), format a text message containing these measurements, and then sending the text message over UART to the PC, to be later visualized in a terminal.
What application are you running on the FPGA board ? You should modify it to read the other Pmod as well.