It should be easy enough to convert H264 videos to MP4 format using programs like Freemake Video Converter or some similar video converter. Considering H264 is often used in MP4, h264 to mp4 conversion is actually sometimes no needed, as you can try to just rename the extension from h264 to mp4, because it already might be MPEG-4 container.
Open H264 file Open MP4 fileA video converting tool for macOS / OS X
A multimedia converter for formats suitable for iPad tablets
One of the many multimedia converter programs for Windows
Easy to use video converter for Mac
Video converting software