Inserting audio post screen recording

Hi Sam and welcome to the E-Learning Heroes Community! 🎉

I'd like to pass along the ELH Forum post that is similar to your request for inserting audio over a previously recorded screen capture. 

The heroes recommend recording in a third-party audio recording software and then importing the audio. 

Once the audio file is inserted into your Storyline project, you can edit the file to line up how you prefer. 

I'd like to pass along this On-Demand Training Video that can assist you as you develop: 

Using Audio in Storyline 360

I hope this helps!