Hi there,
hope you are doing well! ??
To add a heart icon in the menu bar you can follow the next steps.
1. Go to the menu setting on your theme “Appearance > Menu”
2. Select the “Wishlist” option and click on the “Add to menu” button. Now you have the Wishlist link in the shop menu.
3. The last step is to add the icon you want to display in the “Navigation label”, this should be added manually, in my case, I copy one icon from this page.
On this image, I made a visual guide to help you to understand my steps.
And here you have the result.
If you have any doubt let us know and we will be happy to help you.
Have a nice day!