Navigate to Payroll Admin>Payroll Setup>Import csv records
The import type would be "custom record" and the record type is "pay component"
1. The Start Date of the pay component needs to be when the increase is from.
2. The Back Pay to Date needs to be the same as the Start Date.
3. When you do the import mapping options you need to ensure:
a. It is run as an "add" not update
b. You use the "Salary/Wages Pay component form"
c. "Run server script and trigger workflows" is ticked.