HandBrake (https://handbrake.fr/) is a fantastic, free and simple to use tool for reducing the size of video files for use in iSee.
Once installed you simply drag and drop you video file into HandBrake to begin.
Once your video is loaded choose the 'Video' tab and set the average bitrate to 250 (300 if you want higher quality). Also select the location you want the file to be saved to.
Reducing the video bitrate has the biggest impact on file size, but if you want to reduce size further you can also go to the audio tab and set the Quality to 'Quality', and the size to '1', set the Mixdown to Mono and the Samplerate to 24.
Once this is done click the green 'Start Encode' button at the top to encode your file optimised for iSee.