How to set the value of a combobox

Combobox in a canvas section:

The different values are provided by a SELECT ... DISTINCT statement.
I can get a single set value "cValue" like this:

Code:

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var oItem = Lianja.getElementByID("page1.section1.field1");
var cValue = oItem.value;

---

My question:
How can I set the combobox to one of its values by a statement?
For example

Code:

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oItem.value = "FRA";

---

doesn't work.

Thanks for hints!
Georg

item.text = "FRA" will select it.