The steps provided by my colleague above makes your inactive (deleted) customers active again so you can see them. If you followed the steps and they aren't showing up still, my suggestion to you would be to reach out to our support team. This is because they have unique tools such as screen sharing capabilities. Those tools give them everything they need to jump into your account and diagnose whatever your issues are. To reach the support team follow these steps below.
Sign in to your QuickBooks Online company.
Select Help (?) at the top right.
Select Contact Us to connect with a live support agent.
To ensure we address your concern on time, check out our support hours.
If there's anything else I can help with in the meantime, feel free to reach out below. Thanks for dropping by and have a lovely weekend.