Like Chris mentioned in the comments, please provide more information so people would be able to help you. But, here are some pointers that may help you identify and solve the problem:
- Are you using Curlette's
ConfigurationManagerEventSystem
class in your custom event handler to open the configuration XML and return the Configuration object instance? Your solution tree and the app settings value you are trying to get from the config in your event handler should look similar to the one in the screenshot below.

- The config and the event handler DLL should be in the same location and the full path with the name of the DLL should be included in the
<extensions>
element in the Tridion.ContentManager.config
.

- The SDL Web Content Manager Service Host service and IIS should be restarted.
If you have done the above steps, you should be able to read the values from the config. Hope this helps.