How do you wash the formaldehyde lead and the other chemicals off a steering wheel after removing the toxic steering wheel cover?

Formaldehyde is an organic solvent. First use another organic solvent to remove the residue - it may damage the steering wheel plastic so test it first on the back away from where you normally rest your hands. Use a white spirit on a rag or paper towel and then clean this off with alcohol wipes or some metholated spirits also on a rag or paper towel before finally cleaning with lots of water to remove all other solvents.

Put chemical resistant gloves on and where eye protection when cleaning as you will have traces of chemical on the rags that could be transferred into your skin.

Formaldehyde is soluble in water but I'm not sure about this lead compound. If you can't get it to look visibly clean - replace the steering wheel.