You can choose some relatively simple software to do this, such as the commonly used love editing. Shoot customers or something. This kind of software is more suitable for beginners, simple and convenient.

Download the video to be edited to the computer first.

Import videos into love clips. Then import the credits you have done in advance and combine or adjust them.

Adjust the clip and export the video.

Generally, this kind of free software has a disadvantage, that is, the edited video will have its own watermark.