What is the proper alternative for 'credentialize'?
The standard phrase in this context is "establish credibility".
Legitimize.
: to make legitimate
Consider establish (in sense "To prove and cause to be accepted as true; to establish a fact; to demonstrate") and accredit (in sense "To put or bring into credit; to invest with credit or authority; to sanction") and their synonyms.
A little more context would help here, but it sounds like validate would also work here...if your meaning is "to show that there is a valid need for such a product".