(Bb=A#, Eb=D#, Ab=G#, Db=C#, Gb=F#)
Just find the mode and key you want on the chart and set the arp to the major mode in the corresponding key shown on the left… 
-I copied this chart from the Internet, It shows several flat keys at the bottom left, assuming the A4 is like the OT the key can only be set in sharps so I listed the equivalent sharp keys at the bottom just in case…