In order to read dual power on your cycling computer, you must first pair the powermeter as a dual powermeter in the 4iiii App. Do do this, connect both powermeters to the 4iiii App, and tap 'Pair' at the bottom of the screen. After they have been paired as a dual powermeter, you will only need to connect the left powermeter to your cycling computer, which will be identified by ANT+ ID (found in the app or on the side of the powermeter). The left powermeter acts as the transmitter, collecting the data measured from the right powermeter, combining it with the data measured at the left powermeter, and sending it to your cycling computer as one signal. On your cycling computer, you will then see cadence, total power, and L/R balance as metrics.
Section 3.2 of the relevant 4iiii App User Guide below provides more information on dual powermeter configuration: