MEPJ files from Movavi Video Editor are projects and not actually video files, so whilst mepj to avi conversion is possible, you will require all the original multimedia (video) data referenced in the projects.
Otherwise a lone .mepj file just describes the changes done to the original video and as such is useless without the original data.
If you have both the .mepj files and original data, then you can simply load and export your projects with Movavi Video Editor version 23 or higher.
Updated: January 2, 2024