configmap.yaml

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  creationTimestamp: null
  name: test
spec:
  replicas: 1
  template:
    metadata:
      creationTimestamp: null
      labels:
        service: test
    spec:
      containers:
        image: test
        name: test
        ports:
        - containerPort: 80
        resources:
          limits:
            memory: 300Mi
          requests:
            memory: 100Mi
        volumeMounts:
        - name: "config"
          mountPath: "/<existing folder>/<file1>"
          subPath: "<file1>"
        - name: "config"
          mountPath: "/<existing folder>/<file2>"
          subPath: "<file2>"
      restartPolicy: Always
      volumes:
        - name: "config"
          configMap:
            name: "config"
      restartPolicy: Always
status: {}

Be aware that using subPath has the downside of not updating the file when ConfigMap changes.

Unless you restart the pod