For secure lookup, the file you provide is a newline separate list of replacements, like:
100.00 200.00 300.00 400.00
The masking behavior of secure lookup is to cryptographically hash each input value, and replace it with one of the values from the lookup file based on the hash result. So the result with my example input file would be each value replaced with one of those 4 values. There is no need to provide any information about the potential input values.