Lunar Client

Click the dropdown arrow next to the launch game button

In the bottom right, select 1.21.5 and Fabric as your addon.

Click the version settings button next to launch game.

Download the latest Simple Voice Chat mod file from Modrinth from this link. Wait for the popup and just click the green download button.

Drag your newly downloaded .jar file into the mods section of your version settings.

Launch the game, join MerlMC, and click V to set up your voice chat for the first time!