Hi Sky. Down below should be a way to fix this problem. If it still doesn't work, please get in contact with me through Discord. My tag is VortexVisuals#1864.
1. Go down to the bottom left of you Discord and press on the "User Settings" tab. [Shown here]
2. Once in the user settings, head into the tab named "Voice & Video". [Shown here]
3. When here, all you need to do is switch the "Input Mode" to "Push to Talk". [Shown here]
4. When you have done this, you should be able to talk in the voice channels under the category "Police Comms".