The process to unstake your sMAXI is very similar to staking. Open up the staking page of the Maximizer app , and click on "Unstake".
As you can see on the screenshot above, you first need to approve your sMAXI if this is your first time unstaking, so simply click on the "Approve" button. Once the transaction is confirmed, refresh the page, the button should now say "Unstake MAXI"
Enter the amount you wish to unstake or click on "Max", confirm the transaction, and that's it, you just unstaked your sMAXI. You should now have received MAXI at a 1:1 ratio to the amount of sMAXI you just unstaked.