As peer-reviewer, your job is not to make changes or edits in the manuscript you are reviewing. Thus, there is no tracked-changes manuscript upload option. Rather, you are asked to supply a numbered list of issues, which you are supposed to copy & paste into the review form (see How does the JMIR peer-review form look like?). No uploads of manuscripts with tracked changes are expected or even allowed.
Also note that you are not a copyeditor thus you are not expected to correct language issues, typos etc. You are asked to comment on the academic content, method, validity of statements, completeness of references/related work being cited etc.
Please read the instructions for reviewers. We will not be able to award karma credits (see Karma Credits - What are they and how to collect them?) for your review if you do not follow our instructions carefully.