First let us define "Contributor Role" Pi Network defines Contributor role as
Adding members to your security circle by
enabling the Pi Network to secure transactions.
How do you unlock Contributor Role? Per Pi Network FAQ
Pi's Contributor Role becomes unlock for users after you've finished 3 mining sessions as a Pioneer.
In other words, you have to press the mining button or the lightning button everyday and every time your session stops, you have to press the lightning button daily for 3 days and complete 72 hours of mining session
"after 3 days of mining, you will see a new icon of the security circle 🛡 on the home screen of the app which you can click to start. To become contributor, you need to add 3-5 people who you trust to your security circle.
It is recommended that you should build your earning team and add them to your security circle.