You have to create a secret:

apiVersion: v1
kind: Secret
metadata:
  name: testsecret-tls
  namespace: default
data:
  tls.crt: base64 encoded cert 
  tls.key: base64 encoded key
type: kubernetes.io/tls

Once you done that only thing to do is to Refere this secret in an Ingress tells the Ingress controller to secure the channel from the client to the load balancer using TLS:

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: tls-example-ingress
spec:
  tls:
  - hosts:
      - https-example.foo.com
    secretName: testsecret-tls
  rules:
  - host: https-example.foo.com
...

For more reading please visit Kubernete documents at /Services-and-Netowrking/Ingress-tls