I once had an experience when it heavily rained during my camping and all my camping stuff were wet and when I reached home I forgot to dry all of the items. Then when I noticed them I found that the fabrics attached to the camping chairs had Mold/Mildew on them.
As I cannot remove the fabrics from the camping chairs, I am required to clean them using away without removing them from the chair.
So here is the method I followed to clean mold and mildew from my camping chair along with few other methods which other campers suggested.
Allow it to dry in the sun
I first allowed the chair to dry in the sun for some time so that any left Mold will get killed in the sunlight. I usually allow it for at least half a day in optimum sunlight.
Now since you have allowed the camping chair to dry in sunlight, the next is to remove all the mold/mildew/dirt from it using any of the below methods.
If you can find a way to steam clean the entire camping chair without removing the fabrics from it, then this would be the most recommended way which will render your camping chair in the cleanest form.
Add enough alcohol or ethanol into a spray bottle and then spray it on the fabric of the camping chair where there is mold/mildew. Once you spray enough ethanol or alcohol on it, allow it to dry on the sun. You might need to repeat the steps 2 to 3 times based on the result you get the first time. It is also advised to have a small test before soaking the entire chair so that there is no color loss in the fabric.
Add white vinegar to your spray bottle without diluting it. Spray it very well over the place is affected by mildew. Use a cleaning sponge to wipe the entire camping chair trying to remove all the vinegar which is sprayed.
Now take a small amount of this cleaning soap (gentle on fabric), 1 tsp of lemon juice, 1 tsp of baking soda and mix them with enough water. Wash the chair with this solution and rinse it.
Now allow it to dry in sunlight for some time until it dries completely.
Always make sure that you dry your camping gears when it gets wet to prevent the formation of mildew.
I hope this article on cleaning your camping chairs is beneficial to you.