There are a few different ways that you can combine MP4 files into one. One way is to use a video editing program like Adobe Premiere Pro or Final Cut Pro. These programs will allow you to import multiple video files and then combine them into a single project.
Another way to combine MP4 files is to use a video converter program. There are a number of these programs available online, and they will allow you to convert multiple video files into a single MP4 file.
Finally, you can also use a file compression program like 7-Zip to combine multiple MP4 files into a single file. To do this, simply select all of the MP4 files that you want to combine, right-click on them, and select "Add to archive." Then, select "MP4" as the archive format and choose a compression level.