The estimate automatically turned to an invoice when the customer accepted it and there is not a "deposit request" for me to update and send to the customer.

Hello. rob. The deposit request field is only for estimates, so it's no longer available once it turns into an invoice. QuickBooks makes that switch automatically the moment your customer pays the initial deposit. 

With the estimate now converted, you can have your customer make a partial payment against the remaining balance if you need to collect more money. Once you send the invoice, your customer can simply open it, click the Pencil icon through the counterpart portal, and update the Payment Amount to reflect the partial payment. I’ll include a screenshot below so you can see exactly where that is: 

Let me know if you need anything else or have any other QuickBooks-related questions.