"Sing Ho", or "Sing Hoe" is a phrase popularized by Tiktok usually commented under a video where the person is lip syncing to a song. However, they do not know the lyrics and it's painfully obvious they're mouthing the words wrong. Sing Ho is said to mock the person mouthing and tell them to sing the song right.
An expression to say to your friend in praise of something great they did. It refers to the league of cowgirls who sing the Ballad of Joshyberri and coordinate dances to it.