You use your own rom and run it with Ship of Harkinian, which allows you add right stick camera controls, better button mappings, and mods for things such as graphical enhancements.

I don't know how easy it is to find specific community controller configs on deck, but I made one called "Ocarina of Time - Harkinian Deck: C-button Radial, Config Toggle".

Basically it works like this:

Right touch pad = "C-button" radial menu

• Remaps LB, Y, RB, and L3 to a C-button-themed radial menu as Left, Up, Right, and Down respectively.

(You will need to remap your C-buttons away from the right stick in Ship of Harkinian if you want to use it for camera controls. You can just use the radial menu to accomplish that.)

Select Button = "Config mode" toggle

• Summons the Ship of Harkinian Config menu.
• Changes the right analog, touch-pad, and triggers to mouse mode.
• Migrates the C-button radial system to the left touch pad so you can still use it to remap the c-buttons.
• Pressing the button again dismisses the config menu and returns the game to normal "Game mode" controls.

(Don't close the game with the config mode controls active or you will be stuck with config controls the next time you start the game. Be sure to quit the game with the game mode controls active.)

I made a couple tweaks, so I don't know if those are reflected in the community config file I shared.