Open the item and long-press

Then, select 'Edit Item' to open the item editing screen.

Next, scroll to the 'Modifiers' tab.

Select the Modifiers that will be applied to this item.

After that, press 'Save'.

Add an item to the cart and click the three dots. The item options will open.

Select your preferred modifier by clicking on it. After that, press 'Save'. The modifiers will be displayed on the cart screen.