Into the boot (rear) of car?
Remove boot lining if possible and place upside down on absorbent tissue for a few hours, aided with the weight of a brick or something else suitable flat and heavy.
After several more cycles of this method, the tissue should be showing clear. Now try neat washing up liquid, minimum water and a scrubbing brush. The type of fabric will determine the severity of scrub.
Rinse or powerwash and dry.