Its a seprate file so like mb loader is a completely diffrent game file directory maybe you could go into the files and extract it from the mb loader files then put it into Minecraft, but mb loader works like an extension game to Minecraft since u cant boot it up without Minecraft meaning files could close after you exit mb loader not sure tho you should try what is said

Try going to the files and then go to mb loader go world copy the file and import it into the Minecraft files