How to reuse old Apple ID

You can't merge multiple Apple ID accounts.

How do I reuse old Apple ID

Depending on . . . .

Did you delete, see -> How to delete your Apple ID account

How to delete your Apple ID account – Apple Support (UK)

Have you deactivated, see -> How to deactivate your Apple ID account

How to deactivate your Apple ID account – Apple Support (UK)

Scroll to ->  How to temporarily deactivate your Apple ID

Sign in to your Apple ID account page on a Mac, PC, iPhone, or iPad. Then scroll down to Data and Privacy, and select "Manage your Data and Privacy." On the following page, select "Get started" under "Deactivate your account." If you don’t see this option, it means that this feature is not available in your country or region. 

👉 When you request to deactivate your account, you receive a unique alphanumeric access code. Make sure that you keep this access code in a safe place—you must have it to reactivate your account. 

If you forgot the access code, try to contact Apple Support -> Get Support (apple.com)

Do you still remember your old Apple ID and forgot the Password, see this Apple article: If you forgot your Apple ID password

If you forgot your Apple ID password - Apple Support

Then see this Apple article: What to do after you change your Apple ID or password

What to do after you change your Apple ID or password - Apple Support