Create fields for data in Kibana

Hi,
Recently I just make some changes to the logstash and the new data that are flowing into Kibana comes with field.
However, for the data that has already been inside Kibana, obviously it will not be affected by the new logstash configuration.

Is there any way for me to generate fields for those data?
I know one way is to send all the data through logstash again but my concern is that these data will be flowing into Kibana at one shot and it causes the graph to have a big spike.

Thanks!

*I'm using redis to store the data

reindexing is the only way to create a field for documents that miss it. Otherwise, you could create a scripted field that checks for that field: if it exists, it copies the value, if not you set whatever default value you have. And then in visualizations you use the scripted field instead of that new field.