You can report a quest in a two ways:
- In private chat with bot by command
2. In any chat via inline-mode bot.
Next you will be asking for a quest category.
And then you need to choose a quest from the list.
In the end you need to specify a pokéstop where quest was discovered.
The bot will list nearby ones. It’s possible to refine pokéstop list by entering part of it’s title (3 letters min).