I can't find the right alog for directions, so here is an easily searchable set of directions for HAM1 FF.

There is a master switch for the HAM1 feedforward, but it can sometimes cause problems to slam it on and off that way. Instead, you can ramp the input to the feedforward down to zero. From sitemap:

SEI > ISI Sensor Config > [middle of the screen, see attachment] HAM1 ASC FF > L4CINF

This opens a filter bank page with four filter banks. They each have a gain of 1 and a ramp time of 20 seconds. Set all of these gains to zero to turn off the input to the feedforward. Ramp them back to 1 to engage.