Auto-Assign Account Tiers

Is there a way to automate the assignment of account tiers? We've created a field for account tier and can manually assign them to accounts as we go, but this is time-consuming. We are looking for a way for Marketo to automatically assign the tiers based on the account scoring system we've set up. The accounts are being scored, but we can't figure out how to connect the scores with the accounts' tier field. 

Thanks in advance!