You cannot delete the schema directly, rather you have to delete the subject attached to the schema.
You access schema registry url like below to see all the schemas.
https://<schemaregistryurl:port/schemas
So, if your topic name is mytopic, then you must see two schemas in the schema registry with subject named "mytopic-key" and "mytopic-value". Below is an example schema value in "mytopic-value"
{
"subject": "mytopic-value",
"version": 1,
"id": 100423,
"schema": "{"type":"record","name":"User","fields":[{"name":"username","type":"string"},{"name":"phone","type":"long"},{"name":"age","type":"int"}]}"
}
Now if you want to delete this schema, you have to delete the subject.
All the subjects are listed on https://<schemaregistryurl:port/subjects
Soft Delete of all schemas regiseterd against the subject
curl -u username:password -X DELETE http://localhost:8081/subjects/mytopic-value
To hard delete you have to pass ?permanent=true
More options for deletions like, selective versions, latest version can be found on the related documentation at https://docs.confluent.io/platform/current/schema-registry/schema-deletion-guidelines.html