en_tn_condensed/isa/14/25.md

I will break the Assyrian in my land

"I will defeat the Assyrian in my land" or "I will cause the Assyrian in my land to be defeated"

the Assyrian

"the king of Assyria and his army" or "the Assyrian army"

trample him underfoot

This represents completely defeating him.

Then his yoke will be lifted from off them and his burden from off their shoulder

"Then I will lift his yoke from them and his burden from their shoulder"

his yoke ... his burden

The word "his" refers to Assyria.

from off them ... from off their shoulder

The words "them" and "their" refer to the people of Israel.