Open the Instagram app on your iPhone
Find the video you want to save
Tap the share icon or three-dot menu
Select Copy Link if available
Open a video downloader app or website in Safari
Paste the Instagram link into the downloader
Download the video to your iPhone
Save the video to the Photos app if prompted
For your own posts, open the video
Tap the three-dot menu
Select Save to Camera Roll if available
Use Screen Recording from Control Center if download options are unavailable
Stop the recording after the video ends
Trim the recording in the Photos app if needed