Error in running Detection Rules Indicator Match

We are running Detection Rules to search for IOCs in firewall logs (using Indicator Matching). The firewall logs have a field named service. Every time there is a match the following error is seen:

Bulk Indexing of signals failed: object mapping for [service] tried to parse field [service] as object, but found a concrete value

Based on similar topics on this and other forums a solution offered is to rename the field (service).

The present index mapping for the field is:

"service": {
          "type": "text",
          "fields": {
            "keyword": {
              "type": "keyword",
              "ignore_above": 256

Say we were to rename the field, is there a way to rename this field in the existing Elasticsearch indices (old data)?