Reskinning a shamisen can be a complex process, but here are the basic steps you can follow:
Remove the old skin: Carefully remove the old skin from the shamisen using a scraper or a knife. Be sure to remove any remaining glue or debris from the frame.
Soak the new skin: Soak the new shamisen skin in warm water for about 30 minutes to make it pliable.
Stretch the new skin: Place the new skin on the shamisen frame and stretch it outwards with your hands. Use a skin-stretching tool (called a itomaki) to further stretch the skin across the frame until it is taut.
Secure the new skin: Once the new skin is stretched tight across the shamisen frame, use tacks to secure it in place. Make sure the tacks are evenly spaced and that the skin is smooth and free of any wrinkles or bubbles.
Trim the excess skin: Use a knife to trim away any excess skin that is hanging over the edges of the shamisen frame.
Apply a finish: Apply a finish to the new skin to protect it from wear and tear. Traditional finishes include a mixture of glue and water, or a mixture of varnish and water.
Note that if you're not familiar with shamisen repair or maintenance, it's always best to seek out a professional to help with this process, as it requires a certain level of expertise and specialized tools.