1) The first step is to set your DMM to a Transistor Testing Mode it,s important step
2) To Identify it,s NPN Transistor you need to Connect the Negative Lead of the Multimeter with the Negative(N) leg of the transistor and connect the positive lead of the Digital multimeter with the positve leg(P) of the transistor so it will show some reading on DMM so note that reading and do this process again for the other negative leg of the transistor and note the reading if both readings are equal so it,s NPN transistor .
Now connect the Negative lead of the DMM to the Negative lead of the Transistor and the Positive lead of the DMM to Negative lead of the transistor.
when it show "1" as a reading then its Good transistor
when it show "00" as a reading + Buzzing sound then its Bad transistor you need to replace .