On iOS, no third‑party consumer app can truly block another app from opening or stop reinstalls—only Apple’s Screen Time or a supervised/MDM setup can enforce that. For the strongest non‑MDM setup, set a Screen Time passcode, enable App Limits/Downtime with Block at End of Limit, and in Content & Privacy Restrictions set Installing Apps = Don’t Allow, Deleting Apps = Don’t Allow, and Account Changes = Don’t Allow so deleting/reinstalling TikTok won’t bypass limits. If you need “cannot open at all,” the device must be supervised (Apple Configurator + an MDM) to blacklist TikTok; optionally also block TikTok domains at your router/DNS to reduce browser or network workarounds. Which iPhone model and iOS version are you on so I can provide exact steps?