We saw in the latest trailer of Thor love and thunder that how Jane Foster was holding the fixed Mjolnir and Thor was shocked to see it . There are many fan theories around this scene , fans are guessing hard to find what actually could be the possible reason behind this scene . There are two most famous fan theories which can possibly explain that how Mjolnir got fixed .
1 . Sacrifice made Jane Foster worthy
From previous movies of Thor franchise we saw that Jane Foster was astrophysicist . So, she might have gone to study new Asgard site shown in trailer , which is present in Norway . There she might be touring around the new Asgard , then at that time she might have encounter with Gorr the god butcher’s army . Gorr was on mission to kill gods so he might have launched attack on earth to kill Thor , but as Thor was not available on earth so Jane Foster might have come forward to save new Asgard from Gorr’s attack .There is a leaked footage where we can clearly show that Jane is rising up this might be the scene where she was willing to die to save new Asgard .
Then at that moment she might have become worthy enough to hold Mjolnir . She could have accidently summon the broken Mjolnir and if fixed automatically due to Odin’s spell . It went straight to Jane’s hand which might made her next mighty Thor .
2 . Variant from other universe
As we all know after killing Kang shown in Loki series the multiverse began to expand in every direction .So according to some fan theory Jane Foster shown in trailer could be possibly some other variant of Thor from other universe . She might have accidently teleported to main universe due to timeline glitch . This variant must be the next mighty Thor in there universe because the main Thor must have died due to some reason , so she might have summon the broken Mjolnir and it fixed automatically because in there universe Mjolnir might be a living entity
. This is theory very much similar to comic origin of Mjolnir as in comics Odin trapped god tempest in Mjolnir , and it was given to Thor .