I am guessing you probably made the mistake of creating a new account when you wanted to instead change the email address used for the old account. If that is indeed the case, the best thing to do would be to go back to using the old account. You will, however, need another email address when you wish to change the account identifier since the one you just used cannot be re-used for 30 days, and even then that is complicated.
The support article Change your Apple Account primary email address - Apple Support outlines various methods for changing the email address (Apple ID) you use for your Apple Account while retaining everything in your account.
If you have an iPhone or iPad:
1. Go to Settings, then tap your name.
2. Tap Sign In & Security.
3. Next to Email & Phone Numbers, tap Edit.
4. Tap the red Remove button next to the email address, then tap Delete.
5. Tap Choose Another Email Address and enter your device passcode if asked.
6. Enter the new email address, then tap Continue.
7. Enter the verification code that was sent to your new email address. Read this support article to learn what to do if you didn’t get the email —> If you didn’t receive your verification or reset email - Apple Support
8. If you encounter issues with certain services after doing this, this outdated support article may still have useful suggestions --> What to do after you change your Apple ID or password - Apple Support
Refer to the support article Change your Apple Account primary email address - Apple Support :
- If you don’t have an iPhone or iPad, the support article says to, “go to https://account.apple.com and sign in. Then follow the onscreen instructions to change the email address associated with your Apple ID.”
- For general information, and other issues such as changes or addresses not being accepted.
- Note a recent change to the article where you can now change the email address without having to have access to your old email account.
Otherwise how you get access to the old account depends upon why you think you have no access by simply signing in with the account information. We need more information from you about what happens when you try that and what any messages say.