Hi, it depends on where the video was deleted from:
If the video had been added to Lightroom, deleting it moves it to the Deleted album, where it stays for 30 days and can be restored. In Lightroom mobile, open the Deleted album, select the video, and choose Restore. The same Deleted album is also available in Lightroom on the web (lightroom.adobe.com), so it's worth checking there as well.
If you deleted it from the device/gallery view inside the app and it had never been added to Lightroom, Lightroom never stored a copy, so it won't appear in Lightroom's Deleted album. In that case, check your phone's own trash instead — Recently Deleted in the Photos app on iPhone, or the Trash/Recycle bin in your gallery app or Google Photos on Android.
Adobe's help page explains the Deleted album and restoring: https://helpx.adobe.com/lightroom/desktop/using/restore-deleted-photos.html
Hope you can still recover it!