If the mat has compressed areas it should not be used. It is unsafe. If there are many areas where the foam is compressed or collapsed the mat can not be reconditioned.
Many older mats become very hard due to age and years of compression.
They will not meet ASTM standards for g-max values. If your mat is extremely hard it is recommended that you replace the mat. Reconditioning will only soften the mat temporarily and after a few months the mat will return to its original feel. Measure your mat. If the mat is used for competition, it must have a 28' wrestling area and a 5' protection area outside the wrestling circle.