Here's a link to a forum post I made on this topic in July of 2020:
https://cgi.ikmultimedia.com/ikforum/viewtopic.php?f=5&t=25016&p=105365&hilit=sabbath#p105354IMO, the info in that post should go some way to helping you dial in a plausible '70s Iommi tone.
To summarize that link in brief, although I yet hold out hope that IKM will include "based on Laney LA100BL" (and matching cabs), for early Iommi-esque goodness, you
basically want a fairly cranked 1970-ish-era "British"/Marshall-type amp (since the Laneys were basically knock-offs of Marshall back then) which you then hit with a treble booster. In AT5, your best amp options are (IMO) the JH Gold and the British S100 amps (which sound
fairly similar) and the Treble Booster stomp (from the Brian May collection). That said, despite being modeled on a modern "lunchbox" amp, I think the MiniPlex 20 with the right settings (and smacked with the Treble Booster) can also get plausibly Iommi-esque. In all cases, the effects of cabs and speakers are not to be neglected. I would tend to go with the Satch Green, but the 4x12 Closed 25 C would do, and then you can try any sets or combinations of the Brit Green, HiAmp, and Brit Alnico S speaker models.
For more modern Iommi tones, e.g. in Heaven and Hell about 10-12 years ago, you could actually try the ENGL Powerball amp model, since Iommi actually used Powerballs on one of the tours from that period (and the signature amp that Laney put out shortly afterward was rather Powerball-ish
).
As you might expect, there is a great deal of online discussion regarding Iommi gear voodoo -- just how the original Rangemaster might have been modded, the effects of the particular transformers used in the Laneys, various speaker possibilities, changes to pickups at different times -- but a "plexi"-style amp and a treble booster will get you quite a lot of the way there.