How do I sync 2 sliders together?

I have 2 different volume sliders that both control main volume, one is in my game start menu and the other is in my game pause menu. How do I make it so changing one slider changes the other as well, so that when switching between my main and pause sliders both are identical?

I don’t think you should worry about this. From what you say, you don’t have both on the screen at the same time. Store the value somewhere shared (singleton, static, property or similar) and simply update the slider when you display the appropriate canvas. Both sliders can update the value independently.