Fetch JSON Cant attach file for API Update call to 3rd pary

Hi, Im performing a API Call to Fastfield to update a Lookup List, "UpdateLookupList" a PUT call and i need help with attaching the .CSV file to a Fetch JSON pipeline step. there is no errors when i perform a GET request but for the PUT to do the update i need to attach the file to to the update but I dont know where exactly or how to attach it, in JSON URL with the endpoint? request body? or it needs another step to do that, here i attach some screenshots of my pipeline.

Just for some more information, I managed to make to work the (GetLookupList) API call and this was a GET and did not required a file.