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If a person has to work on Sundays, and cannot attend Mass on Sunday morning, Sunday evening or Saturday evening, which are all canonically valid as fulfilling Sunday obligation, then they should speak to their pastor in person and explain the situation, so that he may evaluate the situation and offer some sort of compromise.
Now, regarding this obligation, unless the region has a great lack of priests, there should be a good amount of choice in Masses so that someone who works Sundays is able to attend at least one. If not, then perhaps the person could talk to their boss at the restaurant to see whether they can spread their shifts more during the week so they have some time on Sunday to attend Mass.