ive managed to export the activity graph (which is a TCX) file and open it in excel. HR data is there. Unfortunately timestamp data seems to be gibberish so I cant tell how often the it was recorded. All I could tell what the time interval is not fixed (between 2s to 5s).
Even if I did manage to the timestamps figured out, I need the whole day's chart in excel.
ie, this one:

I can export the raw data (which is a zip file of .fit files), but no idea what to do next. Fit files arent readable by excel.
I tried Strava, which... again, captured HR data only for the activity/run. Tried to bulk export data from there, all it gave me were a couple of GPX files with no HR data :(
If only I could extract raw data from the graphs on the webpages to excel....