to use go here: https://rikukunms2.github.io/MapleSyrupEnglish/
This utility will break down old Mabinogi MML Files to a format that Maplestory 2 can use, including fixing issues with volume and timing.
In the first box, paste your MML file contents (starts with MML@ and ends in ;) into the first box. Then click seperate. You should be able to paste it into the compose window, with each part seperated with the correct tempo markers. Then click seperate This utility does not handle complex tempos, when a tempo changes in the middle of a measure. To fix that, please ctrl + f and search for the letter: 't' and remove tempos that are very close together.
In the event you're trying to convert something that already has seperate parts, begin the harmony with MML@ and then seperate each part with a comma ',' after the last part is pasted end the whole thing with a semi colon ';'
Original Credits to saschanaz: (https://github.com/saschanaz/MapleSyrup)