Follow the steps:

Step 1: When you start the exam, on the microphone check screen, a popup will appear on the top left side of your screen to allow permission for recording. Please click on the Allow button.

Step 2:  You can go to the site setting by clicking on the lock icon from the address bar. From there select the Site Setting option.

Step 3: Navigate to the Microphone option, where you need to select the Allow option.

Step 4: Now reload the exam screen and start recording your voice.