Will be back in roughly a month, I promise. In the meantime, Wikipedia show the meaning of this idiom- “This phrase comes from when radio DJs played vinyl records. The disks had two sides — on a 45 RPM disk, sides A & B. The song that the record company wanted to promote most heavily would go on the A side. So, when a DJ played that side, they’d sometimes say, “And now on the flip side…”, and play side B, the lesser-known track.”