John Wayne is in Star Wars IV A New Hope 1977 and I can't add his credit name.

Crosswalk: See the discussion at https://community-imdb.sprinklr.com/conversations/data-issues-policy-discussions/star-wars-a-new-hope-misc-edit/5f4a7a2b8815453dba9bb7fc where this came up before. I don't believe that this counts as a proper credit for John Wayne, and he should not be listed in the cast of Star Wars.

According to the article at https://www.cbr.com/star-wars-john-wayne-garindan/, sound designer Ben Burtt explained how the character Garindan's voice was generated:

And I was wondering back a few months ago how I did it – because I keep notes and tapes – and I discovered it was an  electronic buzzing which had come off of my synthesizer that was triggered by a human voice. And I listened to it and realized it was John Wayne – I had found some loop lines in the trash from the studio that had been thrown away. So  the buzzing was triggered by some dialog like ‘All right, what are you doin’ in this town’ or something like that.

(Emphasis added.) So it doesn't sound like it was Wayne's actual voice, even distorted, but a synthesized buzzing which was triggered by Wayne's voice. That's pretty far from Wayne having his own voice in the film.

Uncredited voice roles are normally not eligible for IMDb cast listing, but if John Wayne's actual undistorted voice had been used, the exception for voice cameos by high-profile actors would apply (Wayne is one of the highest-profile movie actors of all time). In this case, though, with a synthesized buzzing sound merely triggered by Wayne's voice, I don't think it should count. If Wayne himself had watched Star Wars (and he well might have, since he lived until 1979), I doubt he would have been able to guess where his voice had been used for a sound effect in the film if Ben Burtt didn't tell him.