Click the Find Previous Clip button on the AceText Tower to find the first clip before the current one in the active collection containing the search term. AceText starts with the clip above the active one in the clip tree, going up until a match is found. All clips before the current one in the collection will be searched, regardless of the state of the "all clips in this collection" search option.
If the "loop automatically" option is on, and there's no matching clip before the current one, AceText continues searching the last clip in the collection, all the way back up to the current one.
If the "all clips in all collections" search option is on, then AceText searches the previous collection if there's no matching clip before the current one in the current collection. The previous collection is the one under the tab immediately to the left of the current collection's tab. AceText starts at the bottommost clip in the previous collection, proceeding upwards until a matching clip is found. If not, AceText will continue searching through the collections from right to left until a match is found. If none is found, and "loop automatically is on", AceText starts searching the last collection (rightmost tab), again proceeding from right to left until a match is found or all collections have been searched.