You could’ve done that just checking the checkbox flag that corresponds to Submitting documents after importing.
I guess it’s too late for that, try this in your server console:
$ cd ~/frappe-bench/
$ bench --site sitename console
By this time you should be in the Python console, if so, then run:
for lead in frappe.get_list("Lead", filters={ "docstatus": 0 }):
doc = frappe.get_doc("Lead", lead.name)
doc.submit()
frappe.db.commit() # commit your changes to the DB