How to activate Bad Seed DLC?

[Ixuni]

I bought an Bad Seed Bundle on G2A and idk how to activate/ check if I have that DLC

[kermat_]

Go to your Library > click Dead Cells > scroll down on the page until you see a DLC panel on the right hand side. There will be a button saying "Manage my # DLC". Click it to expand the panel and enable the check mark next to the Bad Seed DLC.

[Fel]

The DLCs are on the right column when viewing the game's page in your library.

To access the zones you need either the teleport rune to access the first zone right from the prisoner's quarter or the spider room to access the prison's depth (not a DLC area but you can access the "morass of the banished" from there)
Here is a map of the zones that include the DLC's zones, this is a pretty big spoiler if you are new to the game:
https://www.reddit.com/r/deadcells/comments/f29i1e/the_new_and_improved_biome_map_bad_seed_compatible/