Play or download the mp3 demonstrating the mask mute for recorder! This may work with other instruments, but they might require even more air to produce sound and be in tune.
Let me know if you try this and how it goes for you! Also, if you know of a real mute for alto recorder, please let me know!
Mystical Strings 
Pingback: How to Mute Your Recorder in 2020 #Music, #Demo, #Musical Monday, #Reblog – My Corner