Volunteered adverbs are provided in this article. The words listed here are commonly found along with the verb volunteered in sentences. This reference page helps answer the question what are some adverbs that describe or modify the verb VOLUNTEERED.
actually, bravely, eagerly
freely, gallantly, generously
gladly, graciously, immediately
kindly, promptly, quickly
readily
Hope this word list had the volunteered adverb you were looking for. In addition to adverbs used with volunteered, other example verb adverb pairings can be found on this site.
You can help by adding more adverbs in the comments. Thanks.