AWX VMware credential default value change

I use AWX with VMware credentials. As per the manual 10. Credentials — Ansible Tower User Guide v3.8.6 there is VMWARE_VALIDATE_CERTS env var defined when the credential is used. I could debug that value is False but i cant find any place where i can change this value to be True.
When creating new VMware credential i dont see any option to select value for this env var.