To compress video size you can use FFMPEG comman line application like this.

ffmpeg -i input.mov -vf scale=1920:-1 -c:v libx264 -crf 23 -c:a copy output.mp4

As a general rule of thumb, you can try compressing the video to a resolution of 1920x1080 or 1280x720, as these are common resolutions used for high-definition videos.