My gauges aren't working after getting my instrument cluster repaired.

The fuel and oil gauges, each one have a sensor that sends a signal to the ECU and then to the cluster. 
When you hook up an OBDII scan tool you can read the values shown directly from the sensor themselves. If the readings are different from what the cluster is showing then there could be an issue with the cluster, however, if the values are the same and both the sensors and cluster are not reading correctly either there is a fault with the sensors themselves or in the wiring. 
 
A hard battery reset can help reboot all the modules including the instrument cluster as well as any communication issues
 
Hard Battery Reset Procedure: