Can & how do i make an mp3 files at iphone ringtones?

[Maestro78]

I owned an iphone 6 with IOS 12.4.8...and i have a cut version and already converted mp3 files (songs) into a AAC files...but how do i add and make this file as my iphone ringtone? I tried the steps recommended but failed...it also suggested that i used garageband app to add the files but it need an IOS 13....so i can’t download it...is there any other easier ways for me to make this files as my iphone ringtones...for example bypassing the garageband method or any suggestion of methods? Thanks