Creating a script for your video helps not only with planning and shooting but also with the captioning process. If you do not have a transcript for your video, you can create one afterwards using a few different methods.
Otter.ai is a free transcription program. It allows you to upload videos (shorter than 40 minutes) and then creates a transcript that can be downloaded.
If you are recording in Zoom, you can enable captions by going to Settings>Recording. In the "Cloud Recording" section, make sure to check the "Audio transcript" and "Save closed caption as a VTT file" boxes to generate the captions.