The Downloads tab will only appear after the activation of WP Travel Pro where the WP Travel Downloads module is bundled so you have to enable the WP Travel Downloads module by going to Admin Panel > WP Travel > Settings > Modules Settings > Pro Modules

Available Options:

• Downloads for Trips: This option allows you to select the download file that is added from WP Travel > Downloads.
• Downloadable Email Attachments: This option allow to selection of the download file which is to be attached in the booking email.

Front-end:

For detail regarding Download Feature, please refer to the documentation link: