How long has it been since you released the single because it takes 2 weeks for the concert to start
If you're stuck "In Production", you can try opening your save file with a text editor, find "SpecialEvents_Manager__EventData" and replace all "Status": 1 with "Status": 0
Save files are here:
Win: C:\Users\*username*\AppData\LocalLow\Glitch Pitch\Idol Manager\data\manual_saves
Mac: ~/Library/Application Support/Glitch Pitch/Idol Manager/data/manual_saves