What dosage of magnesium chloride used transdermally should I apply to help me with a fungal infection on my skin and a bacterial infection on my scalp ?

You could try a number of things. The magnesium gel can be applied 3-4 times/day.   Dosing is not an issue, just put enough on to cover the affected area. You might also paint some iodine on both areas, your scalp and underarms... This can also be done numerous times per day. Iodine kills most bacteria and fungi within 90 seconds of contact. 

Keeping alkaline is a good idea but you can also make a paste of sodium bicarbonate and apply it to your affected areas, alternating with the magnesium and iodine. 

Start with the iodine painting first and do that for a few days, then add one or both of the other things.

If you want more detailed information from Dr. Sircus directly he is available for  consultation :