Note that when you use setFieldValue you need to then save those again back to your dataset as shown in the Wix API Reference.
https://www.wix.com/corvid/reference/wix-dataset.Dataset.html#setFieldValue
setFieldValue( )
Updates the value of a field in the current item.
Description
The setFieldValue function sets the value of a field in the current item. Setting a field value fires an onItemValuesChanged event when the page elements connected to the field have been updated with the new value.
Setting the value of a field in a dataset item does not immediately set that value in the collection that the dataset is connected to. You still need to call the dataset save() function or any other function that performs a save to have the new value reflecting in the collection.
Calling setFieldValue() on a read-only dataset causes an error.
Examples
Set a field’s value
$w("#myDataset").setFieldValue("title", "New Title");
Set a field’s value and save the item to the connected collection
$w("#myDataset").setFieldValue("title", "New Title");
$w("#myDataset").save();
Set a field’s value when the page loads
$w.onReady( () => {
$w("#myDataset").onReady( () => {
$w("#myDataset").setFieldValue("title", "New Title");
} );
} );