Within the custom appendices pages, there is a search option located above the appendices on the screen, just below the page introduction text. This is outlined in red below.
An appendix can be located by typing the name of the custom appendix into the search box. After text is entered in this search box, only matching custom appendices will appear in the appendices list.
This is a useful feature if you want a quick way of locating an appendix when there are a large number shown on the screen.