Hi, Descmh and welcome to the board. Your question can be posed in another way: When Jesus died who did He put in charge? The WTS? or Someone else? What did Jesus Himself say?
The clearest statement that Jesus made regarding this is found in His Upper Room Discourse [which takes up chs 13-17 in John] when He assured that with His departure He would not leave them orphans.
In Jo 16:7, He tells them that when He is gone He will "send Him to You" He identifies this "Him" as the "Helper" or the Holy Spirit. The one who now believes in the Christ and the work He has laid out must then acknowledge that it is this Holy Spirit who now is in '' charge" or "directs" this work
Interestingly, it now becomes a matter of interpretation as to how the Holy Spirit discharges this reponsibility. That He does so directly is plain by Jesus' further words when He says: "He will guide you, teach you..etc''
The WTS, on the other hand, implies, that since they are god's "spirit directed" organisation they are the ones in charge, thus, almost imperceptably, causing a shift in emphasis from the Holy Spirit directly, to themselves - thus making the Holy Spirit an indirect source of authority. This mutation of the words of Scripture is a well publicised trait of their's.
So... in answer to your question, you may gracefully, and tactfully point out to you your WT follower friend, that when Christ died He left no man, or body of men acting as a man in charge. That is the exclusive domain of the Helper. One of the traits that will identify the authority of the Holy Spirit is that He glorifies neither Himself nor someone that the WTS calls "jehover" He will glorify Jesus. Personally. Not as representing anyone, "jehoover" or otherwise. [Jo 16:14]
Now all your friend needs to do is look.
Cheers