How can I re-active the product and service or customer which I'd made inactive ?

Hi there, @accounts-sapient. Let me help you reactive the product, service, and customer that you make inactive. 

We can filter the items in the Products and Services list to see the inactive ones. Please follow these steps:

1. Go to the Sales tab and select Products and Services.
2. Click the funnel (filter) icon. From the Status drop-down, select Inactive.
3. Select Apply.

Once done, you'll see all the inactive items. Click the Make active button. I've added these articles if you need more help in handling your products/items:

• Remove or merge a product or service
• Add product and service items to QuickBooks Online

On the other hand, inactive customers will be hidden in your customer list. Invoices and other transactions will remain in your QBO account and appear in your reports. 

You can also make them active anytime you need them on your list. Here's how: 

1. Go back to the Sales menu and proceed to the Customers tab.
2. Click the small Gear or Settings ⚙ icon above the list of customers. Then select the Include inactive checkbox.
3. Look for the inactive customer on the list.
4. Select Make Active under the Action column.

Here's an article about this for more details: Add and Manage Customers in QuickBooks Online. 

Don't hesitate to comment or post new questions in the Community if you need more help with QuickBooks. We're always here to provide our assistance again.