Use a low charge rate to 'rescue' an over discharged lipo. I use 0.5amp when I have to do this and charge only long enough to get the voltage back up over 6v (for a 2S), then switch to lipo mode and it should charge.

I think you mean amps for NiMh, the volts are handled by the charger unless you're discharging and that should be 0.9v/cell (5.4v for 6 cell pack).

Amp setting depends on the mah, but you can be safe using capacity/1000 so for a 3500mah pach use 3500/1000 = 3.5amps. That will be a good starting point.