Hi, Laura!
Welcome to the E-Learning Heroes community!✨
I understand you are editing the audio in your course. I'm glad you're taking advantage of this tool! To insert silence, select the waveform at the point where you want to insert silence, then select Silence on the ribbon. Another way to do this is to right-click and choose Insert Silence. Please see this article for more details.
If you need further assistance, please feel free to share your file with our team here or privately in a support case so we can take a closer look. We'll delete it from our systems once troubleshooting is complete!