It is uncertain what you meant by 'uploading' csv data.
If you are looking to import data into matlab, you may use the Import Tool. It is found on the 'Home' Tab, under 'Variables' section, by clicking the 'Import Data' icon.
See more details here:
If you were asking about Matlab Online (where you need to upload the file to the internet) you may first upload the file on Matlab Drive. After that, you can import it into Matlab Online using the same Import Tool mentioned above.
