Good grief, Frank. That's why it's a joke. A very kind-hearted joke in this COVID case. It's safe to say the poster maker is riffing on the Practice practice practice punchline.
Practice practice practice doesn't work as all theaters in NYC (and most of the country) are closed. Doesn't matter how much you practice. Nobody is going to hold a concert on one of Carnegie's several stages while the state has closed them due to the current COVID pandemic. Hopefully, that will change in terms of months (if not years).