Cut close to the decal all around, Swish it in a glass of warm water..Let the decal sit, wet, on it's paper back, until it starts moving with gentle prodding with a paintbrush...doesn't move..? leave it alone... looks dried a little, add more water with your paintbrush..
When it starts to move a bit ,,,hold the decal, still on it's backing paper, close to where you want to place it, rest the paper right on the model...carefully push the decal off the backer with the paintbrush one corner at at time until something grabs, the carefully pull the backer out from underneath the actuall decal rearranging things with the paintbrush you still have.....
Slowly