Problem with transposing music when changing time signature

On a song called Under a Glass Moon, there is a part with what I though was in 4/4 time. the measure consists of a half note followed by a half note triplet. But after further listening, it turns out that the measure is in 7/8 time. How would I transpose that measure into 7/8 time but with keeping the half note and triplet? (im guessing that i have to sustain the triplet over 2 measures but i have no idea how to do that.)