I’ve had a Outback. I was of the opinion not the change the A/T fluid ever unless it seems burnt. That was the advice for many decades ago and generally worked. It used to be problems started once the fluid was changed. I have found that this advice no longer works and the A/T on that Outback failed at about 190,000 miles. I have also seen that changing the fluid could have prevented that.
Transmissions have come a long way from the days where the friction material that has gotten into the A/T fluid from the bands and clutch plates wearing can be expected to be tolerated by the rest of the tranny. This is not the case anymore, tolerances are much tighter, valves and passages much smaller. As a general rule change that fluid every 36K if you want your car to last past the end of the warrantee. Not a flush, but a drain and refill. If you want the tranny to last that is. An aside: I ‘love’ how Nissan has ‘lifetime fluid’ in their A/T’s, when asked it is not the lifetime for the car it’s suppose to last, but the lifetime for the transmission.
However in you case I would be somewhat cautious, drain and refill 25-50% of the total fluid capacity one time (which is exactly what a drain and refill does). Doing more may cause unintended things like slipping. Do not do a flush. If you are not handy, but don’t want to bring it in for this, you can use a tube to suck out the fluid from the dipstick (siphon or they sell a hand vacuum pump for this) and replace what you took out - It’s better then nothing.
Also always use dealer tranny fluid, look for deals on the internet on that. It is not cheap.