A corporation is its own entity. Think of how your taxpayer and his neighbor don't file taxes together. The same is true of an S Corp. It files its own tax return. The information about the entity is passed through to the shareholder(s). That's why it is called a pass through entity. That's why all the shareholders are waiting on their K-1, from the preparation of the S Corporation's tax return. They use the K-1 to prepare their own 1040. That is true for any S Corporation or partnership where your taxpayer is a shareholder (participant in the corporation) or partner/member.

And the other issue is payroll. A shareholder that also is an employee (works for the entity) is supposed to be paid through payroll. That means you would have a W2 for them.

"He gave me a rough spreadsheet with some business expenses on it."

Someone is supposed to be keeping all of the business' financial data, running payroll, tracking revenue, perhaps managing sales tax reporting, too. It's not only expenses that you need.

Someone is late filing the corporation tax return. It was due March 15. If this is not the first year of this entity, then what happened to the prior tax preparer? If this is the first year of this entity, then who told him to create an S Corp in the first place?