According to those who hold that the Word at John 1:1 is a person, how do they explain 1 John 1:1 using 'that' instead of 'who' for the Word?

John 1:1 is > In the beginning was the Word, and the Word was with God, and the Word > was God. Many Christians believe that the Word here = a person (Jesus, or the second person of the Trinity), and the reason generally has to do with the grammatical and semantic progression of John's prologue to 1:15. Yet, 1 John 1:1 is > That which was from the beginning, which we have heard, which we have > seen with our own eyes, which we have gazed upon and touched with our > own hands—this is the Word of life. Here, the Word apparently isn't a 'who' but a 'that'. How do those who hold the Word in John 1:1 is a 'who' explain 1 John 1:1's Word being a 'that'?