This is pretty much how every HMT I've purchased "fully serviced" from India arrives. Invariably they have low amplitude and appear to have been lubricated with lard. Some are filthy, and obviously have never been serviced, but others are relatively clean, but over oiled with some unidentified *stuff* of dubious origin.
The one I just looked at this evening, in the trace above, went from around 150 degrees to between 230 and 240 simply by cleaning and re-oiling it, and will probably improve further overnight, so to go the other way, try rodabod's suggestion.
Before you fill it with tar though, I would remove the balance and give it a good close-up inspection. Particularly the hairspring, but also check the shock spring is correctly fitted. If you have access to another balance, try that.
Can try a pen tube (like a bic pen) with the cartridge removed. See if you can find one with a small hole which is smaller than the hairspring collet. A mechanical pencil tube and cap could be more suited.
Or just get a staking set!
Looks like typical banking to me. Crude options for reducing amplitude are heavy oil (like D5) on the balance jewels. Or you could even oil the pallet pivots to make it sluggish.
Better option is a lighter spring.