Can I edit SQLite database file in order to enter a bulk data easily. into a table?
What data are you trying to enter? Several modules in Manager allow batch operations. Find links at the lower right corner: 
I am trying to enter a bulk data to sales invoice and purchase invoice!
You cannot do that. But there is no need. When migrating to Manager from another accounting system, only open (unpaid) invoices need be entered. See these Guides:
https://www.manager.io/guides/how-to/setting-up-starting-balances-for-customers
https://www.manager.io/guides/how-to/setting-up-starting-balances-for-suppliers
I know that, but what is the problem to have access to the database or at lease to have a batch option for all transactions?
One “problem” is that batch operations are already available everywhere they make sense and can be implemented. Another is that many account interrelationships in Manager are automatic, and a single transaction can affect multiple accounts. (An example is a billable time entry, that instantly affects both balance sheet and P&L accounts and is represented in the Customers tab.) In a double-entry accounting system with control accounts, it is not just a matter of pasting in a spreadsheet.
Ok. Is there a way to access the database tables?
@bandak no way. There should be the custom report solution but since there is no database map and no possibility to schedule the queries is almost useless for Business Intelligence at the moment.
You can’t really edit SQLite database directly because Manager stores every object as a serialized blob. There is currently no easy way to bulk import invoices.