go to customisation / scripting / script deployments
Find the script deployment FAM Trigger Pre-Compute SS
Edit, then save and execute.
It looks like the process finishes just about instantly, but it actually takes about 3-4 mins to jump through all your assets and recalc.
You can also create a copy depreciation method (e.g. Straight Line Copy) and switch it to that, which seems to fire this script too.