Use your local microphone in the remote RDP session through the browser.
By default, the microphone redirection will enabled.
To enable sound redirection, you would need to open the Thinfinity® Remote Desktop Manager, go to the Access Profile of your connection, then go to the Resources tab and finally check the Enable Sound option:
When you have the microphone redirection enabled, you would need to allow access to said microphone on your browser as well:
You can copy the file 'web.settings.js' to "C:\ProgramData\Cybele Software\Thinfinity\Remote Desktop Server\DB". This way, your settings won't be lost when upgrading Thinfinity Remote Desktop in the future.