While it is not possible to merge two different user accounts for technical and security reasons, you can manually transfer your data between Hostinger accounts.

To move a website from one Hostinger account to another, refer to these guides:

If your websites is created with Hostinger Website Builder, it cannot be transferred between Hostinger accounts.

You can, however, move it to another hosting plan within the same Hostinger user account if needed: How to Move a Builder Website to Another Hosting Plan.