Hi welcome to the forum.
First thing we need to know is how many coax cables have you connected to the box.
Look round the back you should have two on the outer connections with nothing connected to the inner connection.
If you only have one cable it should be connected to tuner 1 in and you should have a short loop cable connecting tuner 1 out to tuner 2 in.
This will give you two tuner working with some restrictions.
Can you check and post what you find ?