If you already explored most of your world, which includes a lot of the big mountains and the north and south poles, which are new biomes, I suggest starting again, and yes you should bring things from your other playthrough, even if most people recommend the contrary, not everyone has the time to start valheim from the ground up.
But if that's not the case, or you already has a lot of things stored/farmed/mined, it's not needed, just don't go to the superior and inferior extremes of the map yet and you're set. And maybe for convenience you could use the valheim online map, for the last added biome.