In QuickBooks Self-Employed (QBSE), we're unable to manage your client's credits. It's because this is a single-entry bookkeeping program.
I can see how beneficial it is to handle the credits of your clients. Please know that we value your suggestion, so I'll take note of this. Also, I'll submit it directly to our product developers so they can evaluate this preference for future updates.
In the meantime, I recommend checking out this website: QuickBooks UK Blog. It provides you more details about our product improvements. Just click Browse articles under the Small Business & Self-Employed section to view them. Also, you can choose Newsletter signup at the upper right to get the latest tips, advice, and resources to your inbox directly.
Additionally, you can go to Invoices from the left menu. From there, you can edit, duplicate, print, delete, and export the invoice as PDF from the Action column. The screenshot below serves as your visual guide. For more details, see the For you section through this article: Invoices Page.
You can count me in if there's anything else you need. Have a great day, @ram-sapkota.