how to add patch file to dolphin???

[dstruct2k]

That has nothing to do with "OSD" (which stands for "On Screen Display"), that patch just adds the ability to turn "Safe Texture Cache" on/off with the "6" key on your keyboard. This patch has been superceded by subsequent changes to the SVN since then, including the ability to turn this option on/off in the Options screen for your GFX plugin.

If a game requires "Safe Texture Cache" to be enabled, enable it before starting the game. No game should EVER need this option to be turned on and off so often you'd need a hotkey for it.