Example:
So, You can write like this, in function in which you want to update your custom field:

You have two dates e.g. dateA1 and dateB1

def function_name(self):
custom_module_records = self.env[model].search([])
for record in custom_module_records:
for invoice in self:
if record.dateA1<= invoice.INVOICEDATE and record.dateB1>= invoice.INVOICEDATE:
invoice.update({'field':record.custom_field })

FYI:
model: Custom module records.
field: account.move's field that you want to update.
custom_field: custom module's field which you want to update in account.move.