This is very simple.
Just open your Browser and type your vCenter address:
Now find the following on the page:
Vertrauenswürdige CA-Root-Zertifikate herunterladen
Download Trusted CA Root Certificates
After the download, they can be imported into the browser.
Now you’ve to close the browser, usually, and after restarting it you shold be able to access the vCenter URL without getting certificate validation.