you will need to replace your booking-form.php with this https://gist.github.com/markware/a90cb40db4abd4d6023ea131b68512b8
Use the default editor and navigate to the /themes/mykonos/ folder to find the file.
If you decide to proceed with this modification I would suggest you create a child theme, copy over the files you are editing and make the modifications there. This will allow your changes to survive future theme updates. If you directly edit the theme’s files, all changes will be lost once you update.Have a look at this guide to learn more about child themes and how to create onewww.cssigniter.com/ignite/beginners-guide-child-themes/
You can change all theme's strings using Loco Translate(https://www.wordpress.org/plugins/loco-translate/) plugin to change all your strings to your preference.After Installing the plugin you can navigate to Loco Translate->Themes and select your theme. Then if your WordPress language is in English (US) click on the https://goo.gl/qCbywH English language and start changing your stings to your preference.If you have another language as a WordPress default add it from Loco Translate's New Language button and repeat the above procedure for your new language.
Let me know if you need additional help on this.