Hello Mujahidaziz,
You are correct that some tests have a greyed out/disabled print icon. This is because they are only available to be completed online. Not all exercises/tests are available for printing.
To print exercises/tests, you will need to first choose the ones that show you that they are printable.
You should be able to unassign the tests you had already chosen to have another look.
I hope that answers your query.