The following applies to Toad 12, your version might be slightly different.
Connect to the schema which owns the tables, and copy that query from
your email, or wherever, into the editor. Test - how many rows etc do
you get. Make a note.
Select the query, without the trailing semi-colon, and edit->copy to get
it in the clipboard.
Now, Database->Report->Query Builder.
At the bottom, click on the Generated Query tab, and paste your query
into the editor that appears there.
You will need to make sure you don;t have a trailing semi-colon, or it
won’t work from here on in.
Press CTRL+SHIFT+D to synchronise the query and the diagram above it.
After a small pause, the diagram will show the tables involved in the
Just above the Generate Query where you pasted your original query,
there’s a small toolbar. One of the buttons has the text “ANSI” and a
green arrow. Hover over it and you will see the tooltip "ANSI Join
Syntax" - click the button.
The generated query changes to ANSI syntax. If you click the same button
again, it changes back to old-style Oracle syntax.
Next to the ANSI button, to the left, there’s a button with a gree arrow
on it, and the tooltip “Execute Query”. Click it. You should see the
same results on the “Query Results” tab.
Check that the results match your original query’s results, and if so,
do some more testing before putting this into production.
The second button on the toolbar is a clipboard, use it to copy the
generated query to the clipboard ready to paste elsewhere.