How can I Delete certificate via REST API?

You know I didn't even pay attention to the above URL where you got the article. That's for the BIG-IQ, our management platform for BIG-IP systems and application templates.

Are you trying to get/delete the certificate from BIG-IP or your BIG-IQ install, you specified "F5" so I'm taking a wild guess?

This is for BIG-IP: "Content-Type: application/json" -X GET https://xxx.xxx.xxx.xxx/mgmt/tm/sys/crypto/cert

From here: https://clouddocs.f5.com/api/icontrol-rest/APIRef_tm_sys_crypto_cert.html