If 0W-20 synthetic oil is not available, 0W-20, 5W-30, or 5W-40 are approved alternatives. That said, you should change back to 0W-20 synthetic oil upon your next oil change.
Here are some other tips to help you change your Subaru’s oil most successfully:
While changing your oil yourself is pretty straightforward, remember: there’s no pressure if you realize you’re not up to the task. Doing an oil change wrong can cause more expensive (and permanent) damage to your engine than the oil change itself would have cost—so when in doubt, always leave it to the professionals.