I have a suitable pet selected for blessing, but I cannot do it. It says I'm sorry, you don't seem to have a suitable pet. Please choose another. I can only bless a creatu from Reiflem.

If you go to Information -> Creatu Colors on the top right of the page and then select the Elemental Reiflem effect you'll see which species can be blessed. Not all species (even from the right planet) have the effect yet so it's possible all your Reiflem pets just happen to be species that don't have the elemental effect yet.