Open the Minecraft Launcher, making sure you have Java Edition selected on the left sidebar.
Note: This can work with CurseForge users as well, since the Launcher does open in that process.
Rather than hitting
Play, click the
Skins tab at the top of the window.
Click on the
+ symbol to get to the page to add a new skin. Once there, select “Browse” to find and select the skin you want to add.
Websites like The Skindex will tell you whether to use the classic or slim character model, but you can always re-upload the skin if you pick the wrong option. Also make sure to name your skin!
Once ready, click
Save & Use. Now, your character will have the new skin on whenever you play Minecraft!