I have adjusted the "B tension" on old bottom-end Shimano junker derailleur very similar to this one. Though there is no screw for the adjustment, what you can do is drill another hole for the B axle spring, to create a lower tension position that will bring the jockey wheel closer to the cog for better shifting (which I'm guessing is almost certainly the adjustment you want to make, judging by the picture, showing a very sagging jockey wheel on the highest gear.)
Since there is hardly a shred of aluminum to be found in these things, you're drilling though steel, I'm afraid. Use a carbide drill bit if you have one, go easy and slow and take your time. Don't do what I did: namely, don't drill a new spring hole through the hanger, which is a fairly thick plate of steel; drill it on the opposite side, in the B axle housing, if you can. On the hanger side, the new hole hole is retarded relative to the old one (counter-clockwise or backwards rotation around the axle) to bring about more looseness so the jockey wheel is pulled closer to the cogs. On the opposite side, of course, it is backwards: the hole is advanced relative to the old one.
I seem to recall that the "C clamp" on the B-axle is underneath the black plastic cover through which protrude the H and L trim screws. That can be gently popped off with a screwdriver, immediately revealing the axle end with the clamp on it, which can be popped off, after which the whole pivot assembly separates from the hanger, and the spring comes out.
Though this is a fun thing to do, you can replace the whole derailleur with its modern low equivalent: a Shimano Tourney TX-55, pretty much the Shimano bottom end as far as derailleurs go. Anyway, these Tourneys have the angled geometry of the pivot to track left-right in a way that tries to follow the variation in cog size (unlike your SIS derailleur which tracks horizontally), and they have that darned B-tension screw.