We have no choice but to copy the content of the original manual. If there are drawings, the content that can be directly and undoubtedly confirmed from the drawings can theoretically be supplemented.
Another way is to withdraw the application and resubmit it completely, so that you can add any content (you can call the examiner to confirm again). The advantage of this method is that it can make the patent application more complete; the disadvantage is that it costs one more application fee (if the previous one has been paid), the application date is delayed, and there may be new comparative documents that affect patentability.