An Agent can only use the data sources added to that Agent. Having an app like Calendar or Salesforce connected to your Coworker account isn't enough on its own. If a source the Agent needs is missing, it may say it can't reach that app, or it may fill the gap with a guess.
Signs a data source is missing
The Agent says Calendar is "currently unavailable". Missing: Calendar & Meetings.
It mentions meetings or people you don't recognize. Missing: Calendar & Meetings, so it had no real meetings to work from.
It gives account or deal numbers you don't recognize. Missing: your CRM, like Salesforce or HubSpot.
It writes to a Google Doc when you expected your dashboard or canvas to update, or rebuilds the dashboard from scratch every run. Missing: Coworker Artifact.
How to fix it
Open the Agent in Agent Builder. The map on the right shows a Reads from box listing its data sources. (In the Classic editor, open What this agent can do; the list is under Reads and acts via.)
Check that every app the Agent needs is listed. Use the signs above to see which one is missing.
Click Add source (Classic editor: Add data sources) and add what's missing. If the Agent needs to send or update something, click Allow writing to… and pick the source (Classic editor: turn on Can write next to it). See Adding data sources and write permissions to your Agent.
Click Save, then run the Agent again.
You can also ask the Agent Builder in plain words, for example "add Calendar to this agent". It adds the source as a change you can review, and nothing goes live until you click Save.
Still not working? Check your own connection
If the app isn't connected on your own account, the Agent can't use it either. Go to Settings → Data Sources and check it's connected.
Stop it guessing
Add a line like this to the Agent's instructions: "If you can't find the data you need, say so instead of guessing."