The workflow for migrating from Subversion to Git is the following:
Generate the list of repository candidates
$ ./tooling/scm/scripts/gen-repo-candidates.sh > repo-candidates.txt
Create the remote repositories using the ASF self-service git tool
$ ./tooling/scm/scripts/migrate-to-git.sh -r < repo-candidates.txt
Creating a repository can take up to one hour, so do this well in advance
Extract the modules in individual repositories
$ ./tooling/scm/scripts/migrate-to-git.sh -r < repo-candidates.txt
Also validate that the repositories created using step 2 are now live.
Push the local changes to the remote repositories
$ ./tooling/scm/scripts/migrate-to-git.sh -p < repo-candidates.txt