if you look at mirc.ini using notepad, you'll see there are section names wrapped inside braces. Two section titles are [find] and [find2]. One is the search history use see when you press Ctrl+F in a channel or status window, the other is the history in the scripts editor window. Inside that section you'll see several item=value lines that you'll recognize as your history.
You should avoid editing mirc.ini, because you can mess things up if you don't know what you're doing. And if you edit while mirc.exe is running, your changes are often ignored. Your search terms may not go into history if they're not found, so you may need to search for things like 'the' or 'and' to come up with replacement search terms that will eventually force the others to expire.
As for /findtext, it's a way of searching a channel window for text in a way which doesn't put anything into your history. You'd just type in the channel's editbox something like "/findtext and"
If you are brave enough to edit mirc.ini, make a copy of it first, then do the editing while mirc.exe is not running. Then delete all the items in the [find] amd [find2] sections, but not the [section] name too.
