You can use 12VDC but no more. If you have your stepper leads properly identified A+, A- B+ B- and 12VDC won't drive the motor it's likely the amperage the diver is providing isn't enough for your stepper. You can up the voltage but you will have to cut Pin 13 to the UNO or there's a good chance you will fry it. It might make more sense to look for a stepper that has lower amperage needs, Another idea is to look at AccelStepper.h and have the speed ramped up. Starting a motor from stopped can demand a lot more amperage than running it at speed.
Link to a tutorial: https://www.instructables.com/id/Arduino-Motor-Shield-Tutorial/#step1
At the end of this blog there's a link to the shield's schematic: file:///C:/Users/pinya/Documents/Steppers/Motor%20Control%20UK.pdf