If a payroll instruction is not scheduled to appear on this run (or potentially not scheduled to appear on any run by default, as is the case with "occasional" payroll instructions) it will be available to add in manually.
Typically a payroll instruction that won't add to the input sheet is not assigned to any employees. The easiest way to solve this is to add it to all employees, or add it to the single employee you want to use it for. More information about applying to all employees can be found in our How to create an earning pay code article under the section Application Policy under the heading Options within the setup screen. More information about customizing a specific employee's payroll instructions can be found in our How to manage payroll specifications for an employee article.
If the payroll instruction does apply to at least one employee, and it still isn't appearing on the input sheet, ensure it isn't hidden from the input sheet by reviewing our How to create an earning pay code article, section Payroll Input Sheet under the heading Options within the setup screen.