To size the heaters you need the motor nameplate amps at the intended voltage, then look at the chart you show posted inside the electrical cabinet. Pick the heater that covers or is closest to the motor nameplate amps, or follow instructions on that chart if different than what I suggested.
However you need to do a little more digging and considering first before switching to the lower voltage.
Just because the motor can run at a lower voltage doesn't mean the rest of the related stuff in the electrical cabinet is good to go. For example I have a 440V L&S lathe and the motor starters (the whole things, not just heaters) are undersized if running 220V. Similarly you need to evaluate wire size and intended amps if switching from higher to lower voltage. Ideally everything in there is sized for the higher amps that come with the lower voltage, but if they needed to cut cost and knew it was going to be wired for high voltage it may not be safe on lower voltage.
If all that pans out... the transformer is usually to supply control voltage, sometimes also a work light at 110V. Determine what the output voltage should be, then rearrange the input leads or terminals to keep the same output voltage. As mentioned a diagram for the transformer would be helpful, but with a little understanding of transformers and some care you can likely guess and check if it comes to that.
Look for entire machine wiring schematic too, that may be helpful.
