What are you even talking about?
Gällivare exported their ore to Germany through world war one.
They did so otl, and there is no reason they wouldn't ttl.
It seemed you were saying that there was no guarantee that Sweden would continue to export as much iron ore to Germany. But I am glad that we seem to agree that Germany would gain all of the production of Gällivare.
As I've said repeatedly, the best course of action for Germany is not to go to war at all - certainly not an elective war (which 1914 certainly was). Any strategy Wilhelmine Germany pursues in an elective war carries serious risks.
Failing that: An East first strategy which leaves Germany on the defense in the West (which was essentially the dominating approach until Moltke the Younger becomes chief) requires looking at how the general staff evaluated the risks involved with that strategy - principal of which is, arguably, the loss of the iron mines of Lorraine, from whence Germany drew over 70% of its pre-war iron ore. All of which does not factor in the additional, ample iron production Germany gained by seizing Longwy-Briey in the opening weeks of the war in OTL.
The short answer is that Germany kept in reserve some months (I'm trying to track down my source on just exactly how much that was) of iron reserves which could get it over the hump of any temporary disruption of the Lorraine iron fields, which would accord with the idea of the Großer Generalstab to keep that area of Lorraine largely unfortified as "bait" to lure Joffre into a killing sack. It was risky, however. Even recapturing the mines might require some months to get them back into full production. So obviously, Germany must be prepared to make up the difference once its iron stocks run out. Severe economies and recycling in the domestic economy can, from what I can make out, only make a modest dent in the shortfall.
And the most obvious place to do this is in Sweden. The Reich already had call on all of Gällivare's production - but not Kiruna's. In OTL, most of that production ended up being shipped up to Narvik, for sale to the allies, after heavy British political pressure. But if the UK is neutral (even with an Entente "lean") Britain is not in the same position to lean hard on the Swedes, especially against what will be even heavier German pressure to gain *all* of Sweden's iron production.
Beyond that, Germany will have to look to other iron exporters to make up any difference. There were some modest sources in Russian Poland, in the Triasic basin and Kielce district, which will quickly fall into German hands. There are also the mines of northern Italy... Beyond that, fortunately, Germany is not facing a British blockade (at least not of trade), and this opens up other possibilities for trade. If French commerce raiding becomes too grave a threat, a lot can be shifted over to neutral hulls into, say, Italian and Dutch ports.
Likewise, being awash in iron ore is no guarantee of victory to Germany, as should be plain from our own history. Having firm control of Lorraine and Longwy-Briey comes at a horrifically high cost if it brings Britain (and in its wake, Italy and the U.S.) into the war against it. A cost which, in my view, is too much to pay.