Synthetic wig frizz is usually bent, roughened fiber. Conditioner will not heal it the way it might help human hair. You need smoothing, not heavy moisture.
Clean and detangle first
Dirt and product buildup can make frizz look worse. Wash gently, air dry, and detangle from the ends.
Use steam carefully
Steam can relax rough synthetic fibers. Keep the wig moving and test first. Too much heat can change the style or damage the fiber.
Trim destroyed ends
If the last inch is crunchy and permanently kinked, trimming may look better than trying to save every strand.
Bottom line
Fix synthetic frizz by cleaning, detangling, steaming or smoothing carefully, then preventing friction at the nape.