Unfortunately, SVB cannot provide guidance on how to complete FTE calculations. If you have a payroll provider, many of them are providing a PPP specific report to help in this manner.
The reduction calculation would be the difference between the Average FTEs for your Covered Period compared to the Average FTEs in your reference period. For non-seasonal employers, the two reference periods that can be used for comparison are: 1) February 15 to June 30, 2019 or 2) January 1 to February 29, 2020.
In the case of a seasonal employer, the reference periods that can be used for comparison are between February 15 to June 30, 2019; between January 1 and February 29, 2020; or any consecutive 12-week period between May 1, 2019 and September 15, 2019.