What do I have to do if I want to receive my dividend in cash?
In this case, you do not need to do anything.

When will I receive my dividend in cash?
The cash dividend is expected to be paid on June 13, 2022. This later than usual date is due to the technical settlement process related to the scrip dividend. 
Should you opt for the scrip dividend, the new Fresenius shares are expected to be booked into your securities accounts on June 13, 2022, too.

Fresenius Kabi announced today that it has received 510(k) regulatory clearance from the U.S. Food and Drug Administration (FDA) for its wireless Agilia® Connect Infusion System which includes the Agilia Volumetric Pump and the Agilia Syringe Pump with Vigilant® Software Suite-Vigilant Master Med technology. Both pumps are the first to be cleared by following TIR101 standards, which were developed by the Association for the Advancement of Medical Instrumentation (AAMI) in 2021. The product offering for hospitals and clinics enables the centralized distribution of drug libraries, warehousing of infusion data for reporting and analysis, and wireless maintenance and calibration of devices. The clearance is an important milestone for the company’s infusion therapy business in the U.S.