I can understand your concern.
You need to stop wearing those sandals like that. You need to keep the area as dry as possible. And by wearing such sandles those areas will always stay moist which will not let the problem subside.
You can apply candid dusting powder and then wear socks and then over the socks you can wear sandals. Wear them a bit loose.
By night you can apply flucos gel.
Consult a dermatologist for further evaluation and management.
Dr. Anil kumar jain.