Adjusted Employer's Annual Federal Tax Return for Agricultural Employees or Claim for Refund
Form 943-X corrects a previously filed Form 943. It works the same way as 941-X - a standalone return, one form per year corrected, with a choice between the adjustment process and the claim process - applied to agricultural employment tax rather than quarterly payroll.
Whether you deposit monthly or semiweekly depends on your lookback period, not on this form. Publication 15 (Circular E) sets the rule, and it is worth checking each year - the schedule can change when your liability does.
IRS Publication 15File 943-X. There is no amended 943; the correction is a separate return.