To find the hydraulic fluid reservoir for your convertible top, you'll need to consult your owner's manual or a repair manual specific to your vehicle. The location varies slightly depending on the exact model year and trim level, but it's usually near the convertible top mechanism itself, often under a cover or panel in the trunk (boot). It's typically a small reservoir with a cap, and the cap might be marked with a symbol indicating its purpose.
Do not add transmission fluid to the convertible top system. Doing so will damage the hydraulic pump and seals. Use only the recommended hydraulic fluid specified in your owner's manual.