How can this be done, if doable?

Thanks.

 

Carpet cleaner has worked for me

 

Great idea. Thanks!

 

Pressure washer. Use the carpet cleaner or simple green or whatever and then a high pressure rotary nozzle with low volume of water. A short gun makes it a lot easier inside the car. Blast the water off with compressed air gun and use a shop vacuum to collect the water, but avoid sucking directly on the headliner. Blow the water off the headliner, and catch the water with the vacuum. This works great on automotive carpets too, except that there is no issue sucking it up with the vacuum in that case. You'll want to be prepared to get any water that gets under the carpet, which can be a lot of work, so be careful near the edges. I live in an arid climate so everything is dry the same day if I do it in the summer.

If you need replacement headliner fabric, check out https://www.ardmore-design.com/collections/fabrics