Krankenkasse, how do I get them to pay?

Hi everyone. I would like to perform lumbar puncture at a hospital. There are certain tests that I need to be run that the klinik doesn't do. Therefore I'm intending to send my liquor to an external laboratory and do the tests there. Is there any way for my Krankenkasse to take these costs or I will have to pay by myself?

I assume you are in the public health insurance scheme ("Krankenkasse").
In that case, you just show your insurance card to the doctor and they will charge everything directly to the insurer. In case some services are not covered, they will tell you beforehand and get your consent to pay for it.
All medically necessary treatments (as decided by the doctor) are usually covered. Anything you initiate yourself (without it being prescribed by a doctor) is not.
If in doubt, call your insurer for advice.