Blue wrench is just slang for a torch flame. We don’t want to go there if possible :) Just give a little rap on the fastener head, like driving a nail. The object being to break the corrosion up slightly—really just kind of sending a shockwave through the assembly without deforming anything other than the corrosion. Do it after letting the Kroil work on it for a while If the fastener head is soft, like aluminum, take a little care not to mar it up. Just a sharp/quick, but still soft tap with the smallest ball peen you have. Good luck.
Aye aye, Cap'n. I'll do that.