Well first the ambient should not be between 85 and 90
Ambient should be 78/80 and hot side should be 88/90
So how do you provide a hot spot and a cool spot? Usually the hot spot will be provided with a UTH and a thermostat as for the ambient temp it will depends on the room temp itself, and if that is not high enough you will need supplemental heat , it can be a heated room if you have several animals, a heat lamp or a second UTH with a Tstat set to achieve optimal temps on the cool side.