[8FS_Bulau]

In the Mission is see this and which factor would I change?

[Chiefs]
5_Chief Ships.USSEssexCV9 1 0 2 1.0

For the carrier in question, look for an entry like this:
[5_Chief_Road]
14798.93 15003.90 120.00 0 2 8.333333969116211
46297.12 14998.46 120.00

The number, 8.333333969116211, in this example, is the speed in metres per second, which converts to 30 km/hr. So, pick your desired speed in km/hr, convert to m/s, and enter that value into the same spot. A caveat, I think, is that if you open this mission in FMB later, the speed will default back to the 57km/hr maximum.