To Create a New Modifier, Search for the Add-Ons section located on the right side. Click on the Plus sign.
When Creating a New Modifier. Name: Represents the internal name you would like to give to the Modifier. Display: Represents the name that will be displayed on the mobile menu. To allow only one selection, make sure to checkmark the box "Only allow 1 selection"
To assign a Modifier to an Item. Make sure to select the correct Item and Modifier, then click on the arrow pointing left (<--) located on the Add-ons Section. To apply a Modifier to all the Items on the category, select a category and make sure that there are no items select and follow the same process.
To remove a Modifier from an Item. Make sure that the Item and Modifier are selected. Click on the arrow pointing right (-->)