Early Renewals are a funny topic in CPQ because many people think that a unique action is needed to do it. However, Early Renewals are very simple to achieve.
To do an Early Renewal, the easiest path forward is to check the Renewal Forecast and the Renewal Quoted checkboxes on the Contract on the day you want it to process.
This action will stack the Renewal Quote at the end of the existing Contract. You can process it early, though, in the scenario that a customer wants to do that. You can also make any modifications that might apply to that Renewal Quote. An important note, though, is that any amendments will not be reflected on the renewal quote you would have already processed and sent if you can take this action. If you take this step, you will need to make another amendment to the renewal contract.