If you are using Java Edition, you do not usually need to rename the file. Instead, you move the .zip directly into the game's internal folders.
In File Explorer, go to the View tab and check the box for File name extensions . Without this, you cannot change the actual file type. mc.zip
Rename filename.zip to filename.mcpack . Step-by-Step Conversion (Windows) If you are using Java Edition, you do
Right-click your .zip file and select Rename . If you are using Java Edition