Hi Khoudia.
“Cold gelatin” generally refers to a gelatin solution that has already been dissolved and cooled. In some recipes, a gelatin preparation dissolved in cold water is used to thicken or stabilize, keeping it at a low temperature to prevent it from heating up and allowing it to blend more smoothly into the glaze.
You could try dissolving the gelatin in cold water or using a pre-hydrated gelatin mix. It’s important to ensure the gelatin is fully dissolved before adding it to the glaze to avoid lumps.
As for the gelatin leaves, you should use ones with 200 bloom.
I hope this information is helpful, best regards.