Go to https://quay.io/repository/openshift-release-dev/ocp-release?tab=tags to find out the digest URL for the OCP version.

Then run generate-ocp-release-configmap <ocp version> <digest url> <arch>.

For example:

$ ./generate-ocp-release-configmap \
  4.6.19 \
  https://quay.io/repository/openshift-release-dev/ocp-release/manifest/sha256:d74b1cfa81f8c9cc23336aee72d8ae9c9905e62c4874b071317a078c316f8a70
wrote release-image-4.6.19-x86_64-configmap.yaml

Then check in the YAML ConfigMap file.

Based on https://dev.to/baptistemm/openshift-z-patch-upgrade-in-restricted-environment-without-mirroring-quay-io-5em3 but modified to not require oc.