You'd want to set the custom name to a global variable, or a global array object, depending on how many other variables you want to share across layouts.
You can create global variables by right mouse clicking in an event sheet and selecting "Add global variable" from the drop down menu (you can call it "PlayerName" for easy reference). Then, in your events handling name input, once the player gives the OK you can set the global variable "PlayerName" to whatever the player input their name as. Then later on, when you have your dialogue event, you can set the text string as
"Hi " & PlayerName
Global variables are called just as you named them, without any quotes.