I'm wondering if autoignition point decreases for substances when provided higher oxygen concentration.
No, but because of a technical point.
From Wikipedia: The autoignition temperature or kindling point of a substance is the lowest temperature at which it will spontaneously ignite in normal atmosphere without an external source of ignition, such as a flame or spark.
So the definition of the autoignition temperature is based on air not pure oxygen.
For the ignition temperature in general the Wikipedia reference goes on: The temperature at which a chemical will ignite decreases as the pressure or oxygen concentration increases.