Install a skin in Java Edition
Use a 64×64 texture and match the arm model.
Verification status: reference checklist. No claim of completed game-client import tests.
Save your skin PNG locally. Open the Minecraft Launcher, choose Java Edition and the Skins area, then create a new skin. Choose the file and select the correct arm model. Save and use the new skin.
Join a world and inspect the front, back, arm seams and head. If you see missing arm pixels, confirm the Classic or Slim choice before repainting the texture. Third-party launchers can behave differently. This checklist still needs local game-client validation.