We do not currently know of any adverbs for written.
Using available adjectives, one could potentially construct nonstandard adverbs such as writably, writatively, writeably, writerishly, writerlessly, writerlily, writlessly, writtenly or writingly.
Note, however, that these words will not generally be contained within standard English language lexicons.
New Story Writing Game!
Win Amazon gift cards by writing simple stories at Fictish,
a new story writing game backed by WordHippo.