Hints to clean outdoor resin furniture

Wash with a bleach/soap/water solutution

if the chairs are moldy,clorox will not kill the mold.Usw white vinegar.https://www.doityourself.com/stry/proper-cleaning-for-resin-patio-chairs

I wish I knew I have this issue every year myself. Lots of soap and water and hard work

Simple green does usually work well. Probably a scrub brush.

My mom used white resin stack chairs she leaves out all year. Every Spring, she goes out with fish of bleach/dawn/water solution and a scrub brush. She wets entire surface, scrubs a bit (suds stick better than solution alone), then leaves in sun to dry. She then goes back and repeats the wetting/scrubbing process, but rinses them after 2nd scrub. Seems to work well, even after 8 yrs of weather and abuse, she still gets them white!

magic eraser

Greased lightening cleaner/degreaser

Mr Clean Magic Eraser works WONDERS!