You could perhaps Edit > Duplicate… the whole track, Tracks > Stereo Track to Mono then try this script on the duplicate track: https://forum.audacityteam.org/t/need-pointers-on-adding-feature-to-search-pattern/33729/3 Use Legacy version 3 syntax in Nyquist Prompt. If it works, the audio will be trimmed to the bell sound instances only then you can use Analyze > Silence Finder… or Sound Finder… to label.
Otherwise if you change to Spectrogram view in the Audio Track Dropdown Menu you “might” be able to see the bell sound instances more easily.
Gale