Appending to an array that is a field of a dynamic dataset.

I have a Collection called jobs, and I have it linked to a page where I display all the jobs in a repeater. This data set has a number of items, including the job description. I can display all the fields properly in the repeater, but I need to connect a button on the repeater such that when the button is clicked, I append to the item ‘applicants’ (which I have set to an array in the dataset) the currently logged in user’s email or userId. What would be the best way to go about doing this? setFieldValue seems like it would completely overwrite the array, which is not what I want.