The migration for v2018.x to v10.x is not yet available.
The information to migrate from v5 to v10 can be found in the knowledge center. See link below
https://www.ibm.com/support/knowledgecenter/SSMNED_v10/com.ibm.apic.install.doc/migrating.html
As far as upgrade of the infrastructure from v5 to v10 and from v2018 to v10 goes, v10 is a major release and has to be installed on a platform then migrate everything from either v5 or v2018. We provide upgrade process, in that version itself for fixpacks, like v5.0.8 to 5.0.8.8 etc. Major releases have to always be installed.
#APIConnect#Support#SupportMigration