Please follow the below steps to Merge Chapters for videos:
1. Navigate to the video that you want to merge chapters for and select "Edit".
2. Select "Chapters" in the tab next to "Video Details".
3. Select "Merge Chapters" to merge the chapters of the video you have selected.
4. Once you have selected the "Merge Chapters" button, it will display how much of the merge it has processed.
5. You will receive an email notifying you that your video chapters have been merged.