Make Bot here bringing solutions to some of your FAQs 
Before starting the migration process, we’ve noticed that we have a custom app that we can’t migrate from Integromat to Make since it doesn’t exist on Make. We’ve got a lot of scenarios with different modules of the custom app. How can we handle the situation?
In order to migrate the custom app, you will need to contact the app owner. They should either migrate the app to your org in Make or they can follow the 
easy guide attached on how to migrate custom apps.
Migrating custom apps from Integromat to Make.pdf (241.3 KB)
Helpful Links:
Migrating Custom App Guide