The easiest way I've found to edit or delete words in a dictionary with many entries is to go to AppDate/Roaming/NVDA/speechDicts and then open either the default.dic file or a dictionary in one of the voiceDicts folder in a text editor like Notepad where you can use the normal search methods to find the word, or part of a word, pattern or its replacement.
In the file the flag for whether it is case sensative is 1 for true and 0 for false. The second number is the flag for whether it is anywehre, whole word only or a regular expression ... anywehre is 0, regular expression is 1 and whole word is 2.
For example, a entry I added the other day was to get the word dynasty to be pronounced the UK way rather than the American way. This is the line of the default.dic file ... in case it doesn't show up here I'll indicate the tab character with [tab]
If you make edits to a dictionary file then you have to re-start NVDA for the dictionary edits to take effect, but it is often far easier doing it that way than trying to find the word you want to edit in the NVDA dictionary manager.
Hope you find this useful :)