You can find it in your profile menu and can activate the PIN periodically by following these steps:
1. Access the profile page on the top left side of the homepage
2. Select account and security
3. Click Nano Shield
4. Click Require PIN
5. Set the PIN frequency periodically by selecting one of the following options and click save
a. Never
b. After 1 Minutes
c. After 5 Minutes
d. After 30 Minutes
e. After 1 Hour
6. You have successfully activated Need a PIN!
Set your PIN regularly for an extra layer of protection. Enter your PIN every time you open the app within a certain period of time.