Currently, you can only upload existing sound clips via My Rinkel on your computer.
You can set your sound clips for each virtual number.
Go to the My Rinkel app on your iPhone
Click on Settings on the bottom right and then on Call recording or Welcome message. Depending on where you want to set a sound clip. (Want to set up a voicemail? Please click on of the options mentioned above.)
Click on Sound recording or Message. This will take you to all your recordings.
Click on Record sound clip and click on the green icon when you are ready to record.
Click on Done when you are finished.
Set the intended use of the sound clip.