How can I open a Java JAR file for a node on KNIME?

I have a JAR file which has the Java code for a node which I have written for KNIME. Now, I want to test this node but I can’t find a way to open this file on KNIME. Any help on how to view this node on KNIME would be greatly appreciated!

Also, if there is a better way to view/test the Java nodes, that would also really help. Thanks in advance!