Read this page of the Remnant From the Ashes guide to learn whether the game has New Game Plus mode (New Game+). You will also learn how does rerolling a world work.
Remnant From the Ashes doesn't have a true NG+ mode (New Game Plus). Here, you reroll the game's world. You can do this at the beginning of the game or at the end - it will increase the enemies' level. To do this, you need to obtain Red Stone in Ward 13.
Rerolling the world increases the game's difficulty by adding more elite enemies. The regular ones are also more challenging. However, the game will reward you with more XP. You also have an increased chance of finding Lumenite Crystals which are necessary for upgrading items.
Remember that if you decide to reroll the world, you will keep your gear (armor, weapons and mods), Scrap (in-game currency), and consumables. The only thing that changes is the map - it will have a different layout.