Validation is defined as the "confirmation, through the provision of objective evidence, that the requirements for a specific intended use or application have been fulfilled". Unless the development organization understands the specific intended use of the system they have built, they are unable to perform validation. What all software development organizations can do is verification, which is the "confirmation, through the provision of objective evidence, that specified requirements have been fulfilled".
There are ways in which the development organization can perform validation. One case would be if the development organization is also a user of the system, then they can perform validation for their specific intended use. The results of this validation may not be useful to someone with a different intended use. There are also ways in which the users of the system can convey their intended uses to the development organization and the development organization would manage the specific requirements for the intended use and capture evidence that the system meets those requirements.
I would recommend looking at the type of system to learn more. It's very difficult, if not impossible, for a development organization to perform validation of a system that is sold on the marketplace to a variety of customers with various use cases. However, if the development organization is building to the specification of a single customer and gains the deep understanding of how the system is to be used, then they may be able to provide some or all of the necessary validation services.