How do I combine two artists tags?

savuxan and yayuki are the same artist with some of the same works posted across two pixiv accounts. Due to some reason, it seems as if they are trying to make a shift in accounts by directing to this pixiv account

Also don't know where yayuki came from. Name of the pixiv account is muryoudenwa and business email and twitter is also muryoudenwa

The former tag is much older so the posts should be moved over to that one, you just retag the posts with the correct tag and have someone delete the incorrect entry.