DJM 700 beat button broken

Hi, just bought a DJM 700 second hand and its faulty. in the top right of the mixer, just above the tap button and directly below the screen of the mixer, the right beat button is broken. This means I can increase the frequency of an effect but not decrease it, the only way to reset it is to turn it on and off again. obviously this is very problematic when mixing, how much will this cost to get fixed as potentially looking at a partial refund. 

thanks