Hello Ela,

The only way to take the diagnostic test is by clicking on the Start diagnostic button in the test banner, as you see below. However, if you accidently closed the banner or can no longer see it, you don't need to worry. A practice test will always have the same effect as a diagnostic test. So, to gauge your level and adjust your practice sets accordingly, you can go ahead and take a practice test at any time you want.

Do you believe this addresses the issue? I hope this helps but please let me know if you need any further assistance!