how to set default namespace to some namespace using kubectl code example

Example 1: kubectl switch namespace command

kubectl config set-context --current --namespace=<insert-namespace-name-here>
# Validate it
kubectl config view --minify | grep namespace:

Example 2: k8s create namespace

# cli
kubectl create ns test-namespace

# or in yaml
---
apiVersion: v1
kind: Namespace
metadata:
  name: test-namespace