In Minecraft, pressing F3 (many devices require you to hold fn in addition) brings up various statistics. I went to the controls and tried to change this menu to a more convenient button, but could not find the control I needed to change. Where can I find this control, and is it possible to change it? Please keep in mind that I understand little about the game; I am asking on a relative's behalf.
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Based on the information at hand, it seems that you cannot change the function of the F3 key. It is one of the non-configurable controls in the game.
If you will go to the extent of modding the game to see coordinates you can download a mod called Batty's Coordinates PLUS! mod.(linked here:https://www.curseforge.com/minecraft/mc-mods/batty-ui)
you will also need to install the latest forge api and move the coordinate mod into the mods folder. There are plenty YouTube videos that show how to put a mod into the folder and install the Forge client.