You don't do anything to it except spray it with the proper cleaner.

 

2015 XT owner here. 146,000 miles.

I clean the MAF regularly. Many of us consider it part of of regular maintenance. Just spray it liberally with MAF cleaner and let it air dry. That's all. Don't use electrical cleaner or brake cleaner. I like the CRC MAF cleaner spray.

ECU reset is typically done after. This is a simple 30 second battery disconnect. The car may run a little sluggish for the first 50 miles while the ECU relearns. That's normal and expected.

If not already done then consider a walnut blast to clean the intake valves. Carbon on the intake valves has the potential to introduce significant driveability issues. Walnut blast takes care of it.

 

I'd start with the MAF, since it's easier and quicker.

But the throttle body can be quite dirty, especially by 120k miles. It's not all that difficult to do, either. Remove the intercooler, (a few bolts and a couple of clamps) and the throttle body is right there. Another 4 bolts, two small coolant lines, and an electrical plug and it comes right out. A toothbrush, a good sized can of carb cleaner, and some elbow grease and you'll be reinstalling it within an hour.

As a precaution, I purchased the gasket that goes between the manifold and the throttle body, in case the original hadn't fared well. I didn't need it, but as it was my daily driver at the time, the peace of mind having it available was worth it. (Subaru MSRP is $23.73.)

Here's mine at around 60k, before and after. Which reminds me, I'm overdue to do it again.

 

Throttle body cleaning and coolant changes usually go hand and hand. If you want to do them a little earlier 5 years/60k is a good interval. Here is ours at 60k. I did everything when we did the spark plugs on a FB25. Regarding MAF cleaning, I do that more often like every other engine air filter.

 

If you're new to MAF cleaning and throttle body cleaning, you may also be new to the requirement/advantages of "cleaning the upper cylinders". This should be done prior to draining the oil at each oil change. The product is Subaru Upper Engine Cleaner SA459 | Pro Speed Racing. Many brands are available, and the cleaning really does make a difference; the engine runs smoother afterwards.