We are not told. The options are: the angel mentioned in Revelation 1:1 or the “one like a son of man” among the lampstands (Revelation 1:13), i.e., Jesus Christ. As the angel passes on the revelation of Jesus Christ (Revelation 1:1), it is clear that the instruction comes from Jesus Christ. Whether directly or indirectly is not important.
11 saying, “Write what you see in a book and send it to the seven churches, to Ephesus and to Smyrna and to Pergamum and to Thyatira and to Sardis and to Philadelphia and to Laodicea.”