Please annotate all the corrections on the proof using the Adobe Reader commenting and annotation tools (Adobe Help) as highlighted in below example. Make sure not to make direct text edits on the PDF. Alternatively, you can provide the corrections by referring to the query/line numbers in the proof and clearly listing them in a file.
Then, you have to upload your correction in the Production Forum (see How to access the Production Forum for more information).
Inside the Production Forum, go to the "Upload Files" page and complete the file information as per below print screen.
Finally, click on Upload to upload the file. Once the file is uploaded you will be requested to approve or request another proof as per below image.
Note that by approving the Author’s Proof, you agree to Frontiers publishing your article once all your corrections have been incorporated. Please note that by requesting another author’s proof, the production process will be prolonged significantly. You should ONLY request to see another proof if you made major changes to formulas, figures or tables.