In photo is it possible to delete part of a video?

Yes.

1 Tap edit.

2 Move the brackets. Tap Done.

3 Tap save as new clip.

4 Take a throw away video to practice on.

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Rereading your question I can't find a way to delete individual frames, only shorten the video.

It doesn't seem possible in the photos app. However, I think I found a way to do it in iMovie (free in App Store).

Open iMovie and find your video under the video tab. Then use it to create a new movie. You should then be able to edit it a bit.