1. Close MC and all its applications such as QuoteManager, etc and wait till tsServer process unloads.
2. Run QuoteManager.
3. Right click on the symbol and choose Clear Cache.
4. Right click on the symbol again and Edit data
5. Find the tick you want to delete.
6. Delete it.
7. Close QM and wait for tsServer process to unload.
8. Start MC - bad tick will be gone.
Please note, if you reload the chart, bad tick will be returned from the data provider.