Converting .zip to .mcworld on iOS
Solution 1:
Just change the extension from .zip to .mcworld. See here and here.
A description of the file type can be found here:
A MCWORLD file contains files that make up a world in Minecraft, a popular block-building game. It stores multiple files, such as .DAT and .TXT files compressed with ZIP compression. MCWORLD files are typically used to backup a world or transfer a world to another Minecraft user.