The intuitive response to hands going numb is often “raise the handlebars.” But when you raise the bars they also get closer to you because of the angle of the head tube. Then you risk becoming like a coiled spring and having to use your arms to maintain the coil, which actually results in more pressure on the hands. (that is if the bike’s top tube is not long enough) There is a balance between being too stretched out and too compressed. I like to get the saddle height and set back correct first so that the rider is in a balanced position and only needs to use the handlebars for steering, and not to keep themselves from falling on their face. Greg Lemond came up with a formula for saddle height and Grant Petersen simplified the measuring and the calculating. I wrote
these articles about bike fit that might help.