Just a simple little flow that may help you out if you don't have access to any development tools and need to upload some historical data to an asset as a CSV. This scenario recently came up for me so here is the work around:
upload the CSV to an asset (preferably the one it relates to) as a file through fleet manager.
using Visual Flow Creator, pull in the CSV using the read node. Navigate to where the file is located using the elispes in the read file node settings.
use the CSV node to format the data, useually you will have headers so make sure the tick box is checked, otherwise you can manually enter the column names in the text bar at the top of the settings.
use the write to timeseries node to write it to Timeseries after selecting asset/aspect/variable. If you are uploading multiple variables you can just select asset/aspect. However, you need to make sure the variable names match the names in the CSV.
you can import the flow using the attached .txt file.