You cannot join a CSV directly to an existing Trevor query, but you can upload a CSV, save it, and then join it to your query. Just follow these steps:

1. Upload your CSV (note: it must be under 1MB).
   
2. Save your CSV as a new query.
3. In your original query, click join, and then select 'launch custom join wizard'
   
4. Then select 'join a saved query', and join the saved query of the CSV that you saved.
   

Common issues:

You might find that you can't join the tables on the column you expected to use. This is usually due to the data type being different in the CSV and the query. You can fix this by converting one or the other to the correct format using the drop-down menu in the column headers. This might take some testing to get the right format. You can refer to our cheatsheet if you get stuck!