Silicone water repellent help
"Silicone water repellent" is barely helpful information. They are a category of materials which are used in an enormous variety of industrial, commercial and retail applications. Some products react and bind to the surface they are coating, others are simply dried onto the surface. Some cross-link, most don't. A typical consumer fabric silicone water repellent will be "penetrated" by solvents such as acetone, methy ethyl ketone (2-butanone) or toluene; mineral spirits might work. There's no way for us to determine whether these solvents can also damage the fabric or clothing item they are poured onto. Another possibility is to use a fairly harsh (alkaline) detergent, but again I can't say whether the fabric will be damaged. Many of the retail products gradually wear away, diminishing repellency slightly after each wash/dry cycle.