Thanks for your questions.
You can easily add a submenu to your store. We’ve made a video, How to add dropdown, Megamenu, Multi-level menu. Please see the video
Also, to customize lezada theme you can follow our online documentation and video guideline.
Online video guide: https://hasthemes.com/how-to-install-and-setup-lezada-shopify-theme-video/
Online Documentation: https://demo.hasthemes.com/doc/lezada-shopify-theme-v2/index.html
You can follow our guidelines. Hopefully, it will be more helpful for you.