XC90 MY2013 Automatic transmission strikes massively when inserting “D” driving stage

All right, I’ve been having a problem with my automatic transmission for a few days now. Volvo XC90 MY2013 with now 102,000km. When inserting the “D” drive stage, it leaves a noticeable blow, the whole car makes a set, if you don’t press the brake pedal down to the bottom sheet. If you compare it with a manual transmission, you just don’t think the clutch separates properly. The problem occurs sporadicly. Since I bought the vehicle a little over a month ago from a dealer, is the question whether there is a mechanical problem?! My free workshop recommends a drive flushing and oil change. Or should I better go to the Volvo workshop? Thanks and greetings Nico