can you provide a little bit more context? How do you want to search on the lookup? Do you have a search example?
You can always use
| inputlookup value.csv | search foo=*
or you can use the where clause directly in the inputlookup command, which is better for performance:
| inputlookup value.csv where foo > 0
You can find more examples in the inputlookup documentation:
You can not search in the lookup file without specifying a field. A lookup does not run through the indexing pipeline and therefore isnt tokenized and does not have a_raw field for example, therefore you can not search just for text.
But if your csv file has timestamps, you can of course just index your csv file, like you would index any other data.