How can i use a BLDC motor driver to control a brushed dc motor?
If you can't change anything in the drive, you can't: BLDC motor driver are basically 3-phase inverters, that is the output is AC voltage.
If you can reprogram the MCU in the drive, you could theoretically use only two legs and make some kind of an H-bridge that would be suited for a brushed motor. However, I think this would require a lot of works, and the game would not be worth the candle.