Can you provide more information on what it is you're trying to do - that one line question doesn't provide any context.
After loading the log file, we get one log entry as "Connection refused( which is an error message). In our Splunk indexing, we want to suppress these particular ones based on their "Category". How to do this ?
What have you done so far? It very much depends on the fields you have in your data, where this 'Connection refused' message can be found.
In the simple search case, you can just do
your_search... NOT "Connection refused"
but that is not a very efficient search and is the most basic of solutions.
If you want to be able to select to exclude those messages, then you would need some sort of input on your dashboard, but that will depend on what you have and more precisely the workflow you are trying to implement.