Thanks for reaching out divya1512,
It sounds like you're having trouble saving a video using slow motion. We can help.
Let's start by following these steps to Record videos with your iPhone camera:
Record a slow-motion video
When you record a video in Slo-mo mode, your video records as normal and you see the slow-motion effect when you play it back. You can also edit your video so that the slow-motion action starts and stops at a specific time.
1. Open Camera, then select Slo-mo mode.
2. On iPhone 11 models, iPhone 12 models, iPhone 13 models, and iPhone 14 models, you can tap
to record in Slo-mo mode with the front camera.
3. Tap the Record button or press either volume button to start recording.
4. You can tap the Shutter button to take a still photo while recording.
5. Tap the Record button or press either volume button to stop recording.
To set a portion of the video to play in slow motion and the rest at regular speed, tap the video thumbnail, then tap Edit. Slide the vertical bars below the frame viewer to define the section you want to play back in slow motion.
Depending on your model, you can change the slow motion frame rate and resolution. To change slow-motion recording settings, go to Settings
> Camera > Record Slo-mo.
hope that helps.
Take care.