Document API - Replace document (non url)

I am using this API to replace existing documents in my KB.
Here is the code I get from the developer documentation:

curl --request PUT \
--url 'https://api.voiceflow.com/v3alpha/knowledge-base/docs/9999ca7aae7a68be14ada999/upload?maxChunkSize=1000' \
--header 'Authorization: Authorization VF.DM.660fad24ead4233a7a687629.XkesTFHzsL9999' \
--header 'accept: application/json' \
--header 'content-type: multipart/form-data' \
--form file=@abcd.docx

How do I convert the last line of code "form file=@abcd.docx" in the format required in the body section of the API step (see printscreen):
- Enter key
- Enter value or {variable}

Thanks for your help