Unfortunately it isn't possible to change the API ID of a Custom Type after it's been created.
If you need a new API ID, then you will need to create a completely new Custom Type with the correct API ID. Then you can copy your Custom Type JSON from the original Custom Type to the new one. Next you'll need to recreate all your content for this type.
To make the content transfer easier, we offer an Import/Export feature available starting with the Medium plan. You can read more about this here.