Hi,

You can change the report name like this,

<record id="module_name.report_gst" model="ir.actions.report.xml">
    <field name="print_report_name">(object.type == 'out_invoice' and object.state == 'draft' and 'Draft %s.pdf' % (object.journal_id.name) or
    object.type == 'out_invoice' and object.state in ('open','paid') and '%s - %s.pdf' % (object.journal_id.name, object.number) or
    object.type == 'out_refund' and object.state == 'draft' and 'Refund.pdf' or
    object.type == 'out_refund' and '%s - %s.pdf' % ('Refund', object.number) or
    object.type == 'in_invoice' and object.state == 'draft' and 'Vendor Bill.pdf' or
    object.type == 'in_invoice' and object.state in ('open','paid') and '%s - %s.pdf' % (object.journal_id.name, object.number) or
    object.type == 'in_refund' and object.state == 'draft' and 'Vendor Refund.pdf' or
    object.type == 'in_refund' and '%s - %s.pdf' % ('Vendor Refund', object.number))</field>
</record>

This is a sample, change it accordingly,

Thanks