Hi,

Pass form_view_initial_mode as edit in the context.

Sample:

def action_duplicate(self):
    self.ensure_one()
    action = self.env["ir.actions.actions"]._for_xml_id("account.action_move_journal_line")
    action['context'] = dict(self.env.context)
    action['context']['form_view_initial_mode'] = 'edit'
    action['context']['view_no_maturity'] = False
    action['views'] = [(self.env.ref('account.view_move_form').id, 'form')]
    action['res_id'] = self.copy().id
    return action

See: How To Open Form View In Edit Mode From Python Code Odoo

Thanks