Use Windows File Explorer to locate and open the file, or use Restream to change its format if necessary.
Let me know, and I can suggest the best free tools for your specific goal! MP4 Converter for Free | Adobe Express
Use Adobe Express or VEED to upload, trim, mute, or convert the file to other formats.
(e.g., posting to social media, editing it into a project, or just saving it) Do you need to trim or edit it?