When you are moving from ArchiOffice (or EngineerOffice) while using QuickBooks Online, the entire data migration process is handled by BQE consultants, with no download or installation required at your end. After the migration is complete, you are informed to proceed. Your login credentials will be the same as the older online account. You can log into Core and get started there. Check out the Migrating Your Data to BQE Core best practices and FAQs for more. Check out this article for details: Data Migration.
Once the data is migrated, create a new company in QuickBooks Online and sync your Core data to it with just a few quick and easy steps. Please note that you can also switch to Core for your accounting needs.