The main config file has comments for each entry that should make changing the values self explanatory.
Below you can find the locations where the main config files can be found.

${{\color{Goldenrod}\normalsize{\textsf{Fabric}}}}$

The config file is stored per Minecraft installation / instance: minecraft/config/undeadnights.json5
For Fabric when playing singleplayer: you can install the mod "mod menu" and access the config screen

${{\color{Goldenrod}\normalsize{\textsf{NeoForge}}}}$

The config file is stored per Minecraft installation / instance: minecraft/config/undeadnights-server.toml

${{\color{Goldenrod}\normalsize{\textsf{Forge}}}}$

The config file is stored per world: minecraft/saves/[NAME_OF_YOUR_WORLD]/serverconfig/undeadnights-server.toml
${{\color{Orange}\normalsize{\textsf{Note: This is different from Fabric and NeoForge!}}}}$