Hi @san112491,
as @yuanliu said, you have to find the correlation key between main search and lookup: if the common fields have the same name you can use something like this:
<your_search>
| lookup your_lookup.csv common field
if instead the field name to correlate are different, you can use:
<your_search>
| lookup your_lookup.csv lookup_field AS main_search_field
For more infos I hint to read at https://docs.splunk.com/Documentation/Splunk/9.0.1/SearchReference/Lookup
Ciao.
giuseppe