Miguel
tool validations are typically driven by internal company standards and the internal test and validation workflow. I have worked with a number of customers in my past life who were doing business in regulated industries, so I am well familiar with the general principles.
Typically, what you'd need to do is establish what it is that you need to validate regarding the tool, and this in most cases amounts to proving for the right folks in your organization who are responsible for this, that the tool actually does what it is supposed to do.
You can rely on your internal validations, or vendor statement of some sort that certain feature areas are covered by vendor's own manual and regression testing, or a combination. There is really no guideline regarding what you actually need to validate.
We can help you with additional information as you go through the process.