1. Need ifunbox or other soft to download/upload to phone
2. Download /private/var/mobile/Media/iTunes_Control/iTunes/MediaLibrary.sqlitedb
3. Prepare images and put them to /private/var/mobile/Media/iTunes_Control/iTunes/Artwork/Original/00 folder
(use your own naming, for example "deeppurple.jpg")
4. Use Sqlite3 db editor edit 2 tables
4.1 artwork
add line for each artist with parameters id,4,name jpg,4. Where jpg name like u decide in 3
For example deeppurple,4,00/deeppurple.jpg,4
4.2 album_artist
find line with artist name in album_artist column
change value in album_artist_token to id value, for example deeppurple
5. put edited MediaLibrary.sqlitedb back
6. delete MediaLibrary.db-shm and MediaLibrary.db-wal files
7. restart Music.app and enjoy.
ps if u can change image - PLS find and delete files from /private/var/mobile/Media/iTunes_Control/iTunes/Artwork/Caches folder
Cache create automatically