The Fortmatic SDK offers its own end point for logging users out of their Fortmatic wallets.
// Initialize provider
import Fortmatic from 'fortmatic';
import Web3 from 'web3';
const fm = new Fortmatic('YOUR_API_KEY');
window.web3 = new Web3(fm.getProvider());
Users will now once again, have to login via PIN in order to interact with Fortmatic SDK functionality.