There are many organizations that do it. However, the most reputed and most widely used is WES. Every university has a list of transkript evaluation organization that they will accept. So, if you decide to go with anyone other than WES, make sure your university accept that organization's evaluation.

In the case of WES,
Go to wes.org, open your account, and they will ask you the documents that they want from your schools or other entities. Once your schools provide WES with the documents, they will issue you a transkript evaluation.