You should be able to start the classic Outlook from the Windows Start menu. It will show up there alongside the new Outlook, assuming that both versions are installed.
If the classic Outlook is really missing, see https://support.microsoft.com/en-us/office/install-or-reinstall-classic-outlook-on-a-windows-pc-5c94902b-31a5-4274-abb0-b07f4661edf5 . You need a Microsoft Office product (a subscription or a perpetual license) which includes classic Outlook, of course.