The recalculation of the "packages.ref.json" can be triggered by using the Calculate Conan Repository Metadata REST API endpoint, which is only supported for local Conan repositories:
curl -XPOST https://JFROG_URL/artifactory/api/conan/conan-local/reindex
As stated in our documentation, the calculation can be synchronous (the default) or asynchronous. More details regarding the above REST API can be found here.