As an Instructional designer, you need to have some experience recording voiceover. You'll want to take the script that you have written and begin recording your voiceover using a audio recording software. There are free programs out there. Below is a very popular voice recording software.
https://www.audacityteam.org/
After you have recorded the script, edit the unwanted takes and sections. Save your files as individual files for each section.
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