The Testing Back-Log lists the controls whose tests are coming due. Open it from Testing → Back-Log.

What's on it
Every active control on an in-scope unit that's been assessed at least once, except ones the assessor has marked not in place or not applicable this cycle. Each card shows the control, its unit, its criticality and when it's due.
Due now - tests within their lead time, ready to start.
All upcoming - everything scheduled, further ahead.
Start a test
Click Start on a card. The test moves to the first column of the Testing Activity Board.
Good to know
A control whose test is already on the board isn't in the Back-Log. Its next test comes back once that one is completed.
If the start stage on the board is too full, Conform warns you, or stops you starting more until some move on. The limits are in the tenancy settings.
Retests from failed tests are already on the board; they don't wait here.