For your account:
Meet the requirements:
Be 13 years old or older and have your age verified on your Roblox account.
Be in a supported country: Currently, voice chat is available in the United States, Canada, United Kingdom, Australia, New Zealand, Spain, Mexico, Chile, Costa Rica, and Puerto Rico. If you're not in one of these locations, you'll need to go through ID verification.
Enable voice chat in your settings:
Go to Account Settings on the Roblox website.
Select the Privacy tab.
Under Beta Features, find the Enable voice chat option and toggle it ON.
For a specific game (developer side):
Publish your experience to Roblox Studio.
Open Game Settings from the Home tab.
Navigate to the Communication tab on the left.
Toggle Enable Microphone to ON.
Additional notes:
Not all Roblox games support voice chat. Look for the microphone icon next to usernames to see who has voice chat enabled in-game.
You can adjust your microphone and other audio settings in the game's settings menu.
Remember to be respectful and follow Roblox's community guidelines when using voice chat.