Guide

1. Go to the left-side panel and click 'Content'.

2. After that, tick the checkbox beside the videos you want to merge.

3. Head over to the top menu bar, then click the 'Add to Playlist' menu.

4. Subsequently, choose the playlist you wish to use for merging the selected videos.

5. Once done, click 'Save'.

6. After completing these steps, the selected YouTube video will be added to the playlist. To merge them, simply open the first video and play it continuously.