1SE is only available on iPhone and Android, so you’ll need to create your mashed videos directly on your phone. We don't have an online or desktop version of 1SE available for your computer.
If you run into storage issues during the mashing process, try freeing up some space to complete the export.
Once your video is saved, you can move it to Dropbox, Google Drive, your computer, or an external drive to free up space on your device.
For more tips, see How to Take Up Less Space with 1SE.