Typically (by constructing the workflow in my head) I’d try the following:
Connect this node to the List Files/Folders node.
It will create a so-called “Flow Variable” for you, which can use as input for the File Reader node – just connect the red dot to the imaginary top left corner of the List Files/Folders node. You can then input a different file path within each iteration (as supplied by the variable) by clicking the little “V” button in the node configuration.
If you’re just starting with KNIME, I’d recommend to take some time to familiarize yourself with the idea of “Flow Variables”. It’s the way of making your workflows more … well … “variable” 