The web has resources such as planned schedules, cut off dates, etc:

https://www.aarp.org/money/taxes/info-2020/irs-timeline-to-send-stimulus-funds.html

Your client can use the Get my Payment site to see if there is even one coming, or they can settle up on the 2020 taxes as Lisa noted. They filed late for the stimulus process, even though the tax return is timely for its own deadline.