There is no standard migration documentation tbh.
Migration depends on many factors. A few that I can immediately think of:
1. Remedy and ServiceNow both are vast with many many modules.
2. Legacy customizations in Remedy.
3. Customizations in ServiceNow.
I have worked on a very similar project where we did the incremental migration, running different Deltas until cutover.
From my past experience, one of the major challenges was the fact that Remedy doesn't have something like sys_id in ServiceNow which is a tough situation to deal with.
Are you planning to move legacy data, or start fresh, with some transactional data and entire CMDB?
Share some more information about your business case and community can review/recommend.
