If I receive money before scheduling the work. How do I send a receipt for advanced funds/retainer?
QuickBooks Self-Employed does not have a feature to track retainers or customer deposits, lbollin-1.
The program basically offers simple tracking of business income and expenses into the correct Schedule C categories, mileage tracking, and estimated taxes calculation. You can take a look at this article to get more details how the program works: QuickBooks Self-Employed Overview.
In the meantime, you can exclude the transaction if it was downloaded from your bank. You may not also record it manually as an income until the work is done. Please see this article on how to exclude banking transactions: Exclude or delete transactions.
If the nature of your business required tracking of retainers, you'll want to switch to the QuickBooks Online version. It has the ability to record deposits or track retainers.