my purchases disappeared when I changed my apple id?

If purchases disappeared then it sounds like you did not change your Apple ID (which is an email address), you set up a new Apple account with your new address.

Changing/resetting an Apple ID this way will result in relatively little being affected -->

Change your Apple ID - https://support.apple.com/HT202667 - "Follow these steps to change the email address that you use as your Apple ID."

"After you change your Apple ID email address or password, you might need to update your sign-in information with any Apple services you're using" Click on this link to read "What to do after [or before] you change your Apple ID email address or password" --> https://support.apple.com/HT204071

- You may wish to disable Settings > Find My before changing your information, change the information, then reactivate it with the new information.

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Doing it this next way will result in loss of anything purchased with the old account (some mitigation possible with Family Sharing), and disruption of a lot of services until you spend a lot of time trying to get things copied from the old account. -->

Click here to see how to 'Create an Apple ID' = create an Apple Account. --> https://support.apple.com/HT204316

Family Sharing - https://support.apple.com/HT201060

Set up Family Sharing - https://support.apple.com/HT201088

TL;DR: it is not possible to transfer purchases and subscriptions among Apple IDs.