Amtrak has been a lot better about reimbursements than a lot of other transportation entities have been. Early on in the pandemic, if you called your airline pro-actively to cancel an upcoming trip, you only got a voucher, not your money back. So, since I had a number of scheduled and paid-for trips, I played 'chicken' and waited, knowing that at some point they'd cancel the flight and I'd be entitled to a refund. Finally the feds leaned on US carriers to provide refunds that federal law seemed to mandate. (Of course, that didn't help me with Air Canada, who both cancelled my flight and refused to give me anything but a time-limited voucher!)
Amtrak, on the other hand, quickly responded to a phone call made in March requesting a refund for an April trip, and the money was credited back to my credit card quickly. They initially limited the time period where you could just call and get a refund, no questions asked, not knowing how long the pandemic was likely to last, but kept pushing the date out as things dragged on. At the moment, I think the rule is if you cancel within 14 days of your travel date, your payment is re-credited to the means of payment you used with them, for any trip booked by the end of March. I fully expect that, like earlier deadlines, this one will likely be extended.
And, as was noted above, if you made your reservations separately for the inbound and outbound, or two different legs of the inbound or outbound trip, you'll have to cancel them individually--cancelling one won't automatically get you a refund for the others.
Note that Amtrak Vacations has its own separate cancellation policy, which is to only provide vouchers good for two years, which can be transferred to family or friends if you can't use them. (Also, if you buy their ripoff insurance, the vouchers don't expire. So maybe it's not quite the ripoff that it used to be...) So, another reason to do your own booking, even if it is a little more time consuming.