The Resurrection of Kang The Conqueror
His return from out of the Beyond Zone explained from the scrapped Avengers: The Kang Dynasty by Micheal Waldron and Jeff Loveness.

The Second Coming of Kang:
After Kang the Conqueror’s fight with Antman, Kang was hurled and shrunk into the Multiversal Engine Core. Kang went subatomic into several thousand dimensions.

Kang ends up exiting out of the multiverse. He enters a “void” that is known as the BEYOND ZONE.

Kang finds himself trapped In the Beyond Zone. The Beyond Zone is strange reality surrounded by an extremely strong probability storm.

The energy from the probability storm gives him the ability to create multiplicity of himself (clones)…similar to what Antman experienced.