How to add/remove virtual server in existing ASM Policy?

If you are using a default policy association like screen above, you probably have an ASM policy started by an LTM policy. This is an example using iControlREST and cURL, to remove ASM policy from vs_https.

curl -kv -u "admin:admin" -H 'Content-Type: application/json' -X GET  https://192.168.1.245/mgmt/tm/ltm/virtual/~Common~vs_https/policies?\$select=fullPath |json-format

{
  "kind": "tm:ltm:virtual:policies:policiescollectionstate",
  "selfLink": "https://localhost/mgmt/tm/ltm/virtual/~Common~vs_https/policies?$select\u003dfullPath\u0026ver\u003d13.0.0",
  "items": [
    {
      "fullPath": "/Common/asm_auto_l7_policy__vs_https"
    }
  ]
}

curl -kv -u "admin:admin" -H 'Content-Type: application/json' -X DELETE  https://192.168.1.245/mgmt/tm/ltm/virtual/~Common~vs_https/policies/~Common~asm_auto_l7_policy__vs_https |json-format

I hope it helps.