Hello there!

You might not be able to find inactive customers because you forgot to check the box that says "Include inactive."

This option allows all inactive customers to show up on the lists, and you can choose to make them active or not. Let me help you with this.

Here's how:

1. Go to the Sales tab.
2. Select Customers.
3. Above the Action button, click the Gear icon.
4. Tick the box Include inactive to show the inactive one in your customer lists.
5. Go back to your customer lists and find the customer whose beside their names have the word deleted.
6. Click the Make active.
    

You might want to learn about merging customers, you can read through this article: Add and manage customers in QuickBooks Online.
 

The Community will always be here, willing to assist you with making inactive customers active again. We'll be happy to help. Have a good one!