A strong capital “S” in cursive doesn’t come from forcing the shape—it comes from controlling the motion: a steady entry, a smooth middle turn, and an exit stroke that helps the next letter. Once you practice those moments separately, the whole letter usually falls into place.
Keep your sessions short, correct one flaw at a time, and focus on consistency over perfection. With a little patience, your capital S will stop feeling like a problem letter and start looking like a signature you can actually trust.