i am not an expert.. but here is what i have had luck with problem sheds..

when i got Freckles, she was in a shed, but still had old shed on her.. i soaked her in a shallow bin of water kept warm with heating pad on low... she LOVED that soak.. when i picked her up, she started to work against my hand to get that old skin off.. it worked well for Freckles, as all the shed (s) came off..

i have also used a moistened wash cloth for other rescues with shed issues after a nice long soak..
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Cilene
2 kenyan sand boas
2 redfoot tortoises
3 box turtles (florida, eastern, ornate)
2 sulcata tortoises