To add food legends:

Step 1: Visit Setup > Menu Setup.
Step 2: Search for the item you wish to edit using the search field.
Step 3: Click the Edit button.
Step 4: Scroll to the Food Symbols section and select the appropriate symbols.
Step 5: Click Update.
Step 6: Finally, click the Refresh POS & Online Menu button.

Note: If you are integrating your menu with Zomato, make sure you select either 'Veg' or 'Non-Veg' for all food items you wish to display in your Zomato menu.