What does this lever on the left side of the carriage do ???

If the lever moves forward and back, it might be the Tab set/clear...but if it results in nothing, it might have some mechanism out of adjustment...
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I also discovered that tabulator works regularly, kinda of. The scores of moving tabs on the rear of the machine are slow and crusty due to dust and decades of disuse. Cleaning and with some delicate coercion, they works, I have to set cotton swabs and ethanol aside and put my toothbrush at work with some serious  isopropyl alcohol.
 

How are Tab stops set and cleared on these early H-2000 ?

Looks like the early ones (1-3 years or so) did not have a Tab set/clear lever on the left side.

Maybe those had manually set Tab stops along their backs...
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Hi typists. Just to inform that I managed to have a fully working Hermes 2000 with very little effort. The machine, as already reported, was professionally  refurbished before, most likely by the reseller that sold  the machine to the previous owner; she used the machine sparsely in the last decades. Cleaning the dusty external panels and the basket took just a little while, but typebars were dirty inside the O and D and other closed typefaces,  other than that internally the machine was almost   clean, just a little dust. Changing the ribbon was the most difficult task (where are my long tweezers when I need them?) and apparently Olivetti ribbons are OK for Hermes 2000s as well.  The original ribbon metal spools are gone unfortunately, and afaik they sell for a disproportionate price, so plastic it is . There are glossy black spool covers so the great aesthetic of the machine is not spoiled. The rotting old ribbon was... rotting,  but inked great, ribbons used to be   higher quality back then. The rubber feets of the machine appear new (obviously they were swapped  back then). The carrying case is in good conditions and even better after some vinylic glue took care of a corner. Given it is almost 90 years old the machine is in great working condition.
The bell is another matter though. It didn't work, and the bell did not sound even if hit by a metal tool. The bell hammer appeared to be alive and kicking, but could not be activated by the moving platen as for some reason the pawl appeared to have been bent too low. The bell's retaining screw appeared to be welded solid to the bell and my cheap watchmaker and expensive electrician small screwdrivers could not move it. So I measured the screw with my spark plug gauges and out I went;  sourced a couple of  good thin flat screwdrivers (0,4  and 0,5 mm thick). With the help of a little WD oil and the 0,5 mm screwdriver (look I know you hate WD-40 and I have better alternatives  but that drop  was enough) the screw was free. I could  not believe the noise that tiny screw screeched out when it started turning, but the bell was finally (and most likely for the first time in almost a century) unlocked. I don't know why the hammer's pawl  could not be reached by the protruding part under the carriage  but that was it, so i bent it a little upwards (it was pointing downwards..) and prolonged the pawl wit half a centimeter of plastic tubing, so now the bell is activated regularly. Either the carriage  used to go one or two millimeter lower (unlikely) or there is some setting screw I could not see, anyway  the 'upgrade' is reversible in a few seconds until I know better, fact is there is precious little tech manual out there on this model to download or buy. It works fine though, very happy to type with it, feels snappier than the famous 3000 /Media3 sister and is more conventional to operate, I feel very much at home with this machine. Did I mention it is beautiful?