Before using the ThreatExchange API, you'll need to create a Facebook app.
Please see the Terms and Conditions -- depending on your company, you may wish to obtain signoff from your company's legal team.
... if you haven't already done so.
The name ThreatExchange appears with a green checkmark, and you see the subproducts "Descriptors", "Tags", etc. in addition to "App Review" which you had seen up until now.
Do a power-search for tag "testing" -- you should see results.
Welcome to ThreatExchange!
Next, continue with the Getting Started page!