If you are using the Splunk UI to configure your inputs, then the location of the config files is based on the setting you select while creating the input. In particular, the setting for App tells Splunk which App to use when storing configs. The Apps are located in Splunk_Home\etc\apps. In the App that was selected when creating the input you will see a "local" folder which will contain the config files.
If you are using apps downloaded from Splunk, then the data used those Apps are typically configured inside that App, which can be found typically by name in Splunk_Home\etc\apps.
If you don't remember which App was selected when the input was created than you can use the Splunk UI to find it. Go to Settings, Data Inputs, Files and Directories for a list of file inputs. This list will also tell you which index is used for that input. It is possible that you are using inputs other than "File and Directories", so review the list of possible local inputs. There is a column for the number of inputs to give you a clue as to what type of inputs you have for those input types.
If you have custom field extractions or other UI generated transforms, then you may file those settings in the user context in Splunk_Home\etc\users under the user that created them.
