There have been a lot of good shooters and ball players mentioned but let's look at the problems Iowa has had the last few games which is mainly rebounding and some scoring droughts because of shooting and turnover differential. So better rebounding and or more scoring and more consistent scoring.
I think if you can only add one person they would need to be able to help a lot on the boards especially the defensive boards where the hawks have been getting clobbered. And they would need to be a decent scorer.
If you can go back in time like some people have said I would say that Chris Street, one of the best all around players at Iowa in a lot time, or Reggie Evans would solve both the rebounding and scoring problems. Reggie would get lots of bounds and put backs and he and Garza could both be on the floor with them moving in and out of the low post. Same with Street except he could also score from anywhere, he and Garza with 3 very good guards would be almost unstoppable.
Now, for much more recent players JBo lighting up the scoreboard could overcome the 6-8 extra offensive rebounds we give up that leads to a few extra baskets. And I am talking Jbo at the wing in a rotation with CJ and JW, and with JBo at the point with Connor and some JT, and Garza, JW, and Kreiner, and a little Pemsl at the 4-5.
And in actual reality going forward, the hawks havent been getting a lot of fast break points so all 5 need to turn, block out, and crash the defensive glass come tourney time. CJ and JW need to get boards and the guards need to get loose balls and long rebounds.