You can handle this several ways:

Method 1: If you're creating items one by one

1. On the page you are doing the work, create a local variable of a list of whatever items you want to manipulate eg \"tempList\"

On page load load whatever is the existing state of the list from the database into tempList
Add items as you create them to the list
Write the result back

Method 2: If you have a list of items you want to add eg newItemsList

As above but:

Create another variable called \"index\" and set it 0 on page load
On your action to save the result, create a loop that:
Checks to see if index is less than the no of items in \"newItemsList\"
If it isn't add the the item at position \"index\" to \"tempList\"
Increment \"index\"
<End of loop>
Write the final state of tempList to the database

Method 3: Create a custom function

This is a bit trickier but actually worth the effort to learn as it is the answer to many things you may want to do in FF. Its made massively easier because of the AI code helper that writes the code for you. Name the function, make sure you specify the inputs correctly with the right datatypes and as lists, the same with the outputs and then just type what your trying to achieve into the prompt and watch is come up with something that works for me almost always, straight away. Use the web version of FF and you can test your function directly.

HTH

Add a list of items to set?