I have an output table that has several cells with zeros and I wanted to remove those cells through either deleting or filtering. Table looks something like the below
Not sure what your error is but in Row Filter node you should use flow variable currentColumnName which is created by loop. This way your column to test in Row Filter node is your current column in iteration. See image.
In general you should play around with it a bit. Read node descriptions carefully and understand how it works. First try without loop and with one column only. When you manage to do it then add loop and other things