First of all
You need to check if the models aren’t in .zip extensions file, activate the “show extension file” in the file explorer
After that just delete the “.zip”
Now, you have two paths
Premium user :
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in mc click open skin editor>file>open>select model
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file>export>export mode:model>export>paste
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on a world press G (you can change the keybind) and models, select the exported model
No premium :
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open the skin editor in the menu and select the model
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test in game > select the world you want to play
The no premium users can’t export the model but you can tell a friend who have bought mc to export one model and send you the exported model, you just need to put it in .Minecraft>playermodel