First need to prepare the csv file to import. Prepare the file with fields which needs to be mapped or import and make sure that the csv file have mandatory fields.
Mandatory fields to import an FAM asset :
ID
Name
Asset Type
Asset Original Cost
Residual Value
Depreciation Method
Asset Lifetime
These are the mandatory fields needs to be in a FAM asset csv file.
Setup > Import/Export > Import csv Records > Import type > Custom records > FAM Asset > Select csv file > Next > Add > Next > Do the mapping process properly > Next
Prepare the Depreciation History file to be imported after FAM Import, do the same procedure of importing using Import Assistant. After Importing the Depreciation History records run the script
Customization > Scripting > Scripts > Filter > Scheduled > FAM Trigger Pre-Compute SS
Under Deployment subtab : FAM Trigger Pre-Compute SS > Edit > Status > Not scheduled > Save and Run