Im recording a concert and using an xlr from mixer into my Canon XHA1, should I use the +48V ? also should i use mic att?

any other advice would be great thanks

The 48V phantom voltage is used only to power a condenser-type microphone. There is no purpose in using Phantom Power when not using a mic, and it should be disabled. If you're using a feed from a mixing deck, the typical output is normally +4dB, so I'd recommend trying the Line setting first. If that's too low, then go the the attenuated mic setting. However, if you're using the mixer connected to your own microphones, then, yes, you will likely use the Phantom Power for the mics, but the voltage will not be fed your camera.

Note further that not only do you not NEED 48V phantom power when receiving audio from a mixer (etc), but in many cases, feeding 48V phantom power back into a mixer output will cause it to operate improperly and distort the audio signal (at best), and worst, it may even damage the mixer (the output capacitors specifically).