Hi! We don't have an existing conveter script – although it'd be cool to have, if you end up writing one and want to share 
Assuming you've used the (semi-)manual relations UI to annotate dependencies, here's the format that Prodigy will produce: https://prodi.gy/docs/api-interfaces#relations It should give you all the information you need, so it should mostly come down formatting it as columns, depending on the CoNLL-U specification you're using. The easiest is probably to just loop over your list of "tokens" and for each of them, check if it's the "child" of an annotated relation and if so, get its head and label.