Here's the instructions for Synthropol LF (that's the low-foaming version made for HE washers). Note: you have to have the water at 140F (60C). If needed, add some boiling water to the machine before you start.
https://prochemicalanddye.net/auxili...hrapol-lf.html
For future reference, I do wash jelly rolls. I set my washer on cold, hand-wash/gentle cycle and then just dry partway in the dryer on low. I've only used Kona & Moda jelly rolls, but those don't shrink or unravel on me. The other option would be to hand wash them in a sink and let them air dry. With black, especially, I think it's worth it.
I have not used Synthropol on a finished quilt. One thing to consider is whether the fabrics you selected will shrink at different rates when exposed to the hot water. Depending on the thickness of the cotton yarn & the density of the weave used in each fabric, they could produce different rates of shrinkage.