How to provide in-text citation for Appendix
The easiest solution is to provide a reference to the Appendix (e.g., "for further details, see Appendix) wherever the additional information is relevant. If your Appendix contains several different types of content then subheadings would be helpful. Then, you can reference the specific Appendix sections in your text. Seeing as you're at the copyediting phase now, you likely don't have many other options.