How to turn the video in my mobile phone into a slow-motion video, and what software is needed (my mobile phone is Android)

It can be set by the software "Quick Shadow".

The solution to this problem is as follows:

1, first open the phone and click to open the "Quick Shadow" app.

2. Then click "?" At the bottom, No, import the video at a variable speed (the video quality will not be compressed).

3. Click "Variable Speed" in the editing tool below.

4. Then drag the speed change bar. Less than "1X" will slow down, and more than "1X" will fast forward and accelerate.

If you only want to change the speed of a clip for a few seconds, you can "split" the video first, split the picture to be changed before and after, select the clip, and then change the speed.

6. Finally, after all the speed changes are processed, click on the upper right corner to export the video.