Failed to authenticate user [elastic] after changing environment

Elastic Stack Elasticsearch
2

Update: I have tried the method proposed by TimV to add a new superuser and resetting the password for other users. This is the error that I received.

{
  "error" : {
    "root_cause" : [
      {
        "type" : "unavailable_shards_exception",
        "reason" : "[.security-7][0] [1] shardIt, [0] active : Timeout waiting for [1m], request: indices:data/write/update"
      }
    ],
    "type" : "unavailable_shards_exception",
    "reason" : "[.security-7][0] [1] shardIt, [0] active : Timeout waiting for [1m], request: indices:data/write/update"
  },
  "status" : 503
}