My 2021 K5 car mileage

My 2021 K5 car has over 200,000 kilometers on it. I haven't changed the transmission oil, nor have I found the original owner. I started noticing minor issues with the transmission; for example, if I press the accelerator while stationary, it engages gear roughly and shifts unevenly between gears, but if driven normally, everything is fine. However, acceleration in a straight line and on highways works perfectly. What do you suggest? Should I completely change the transmission fluid electronically along with a conditioner, or should I do a partial change, one liter out and one liter in? Until when should I completely replace it? Please reply