Hi,

First, you need to define the button in the XML

<button name="action_send_report" class="oe_highlight"
        string="Send Mail"
        type="object"
        help="To send part ledger"/>

Next, we need to define the py for getting the attachments,
Function for sending attachments in the mail

def action_send_report(self):
    """Send partner ledger report as mail"""
    report = {
        'docs': self,
    }
    record = self.env['ir.actions.report'].sudo()._render_qweb_pdf(
        'module_name.record_id_of_ir_actions_reort', self.id,
        data=report)
    ir_values = {
        'name': 'Partner Ledger',
        'type': 'binary',
        'datas': base64.b64encode(record[0]),
        'store_fname': base64.b64encode(record[0]),
        'mimetype': 'application/pdf',
        'res_model': 'your.model',
    }
    report_attachment = self.env['ir.attachment'].sudo().create(ir_values)
    email_values = {
        'email_to': self.manager_id.work_email,
        'subject': "Partner Ledger",
        'attachment_ids': [report_attachment.id]
    }
    mail = self.env['mail.mail'].sudo().create(email_values)
    mail.send()

Hope it helps