iPad Pro wifi to cellular

Well, if it was a cellular enabled device, it will always be a cellular enabled device. If it is capable of using cellular data, the only step required would be to contact a cellular provider and enable the service with their help.

Out of curiosity, what is the model number at: Settings - General - About - Model = ??

SarahLangemann wrote:

I recently bought a refurbished iPad Pro. It was originally a cellular tablet. And turned into a wifi tablet.

can this be reverted back to a cellular device?

You would need to contact your phone carrier to set up cellular data on it.