How to Open a Mod's Config Screen In-Game
Reaching the Config Button
Open the mod list from the title screen, then click the mod whose settings you want to change. Expanding the entry reveals its details panel. If that mod supports in-game configuration, a config button or gear-style icon appears in this panel. Not every mod offers one — mods without config support simply won't show the button, and you'll only see their description and links.
Changing Settings
Click the config button to open that mod's own configuration screen. The layout here is defined by the individual mod, not by Mod Menu, so it varies: some use sliders and toggles, others use text fields or category tabs. Adjust the values you want, then save or confirm using whatever button that screen provides. Many configs apply immediately, while a few require you to leave the world or restart the game before taking effect.
When No Config Button Appears
If the button is missing, the mod either has no config screen or stores its settings in a file you edit manually. In that case, use the links shown in the mod's details panel to reach its documentation. Also remember that config screens are easiest to reach from the title screen, before loading a world, so you can set things up without interrupting play.