Use the adverb hereby to mean “as a result of what I’m saying right now.” For example, your bus driver might announce, “All cellphones on the bus must hereby be turned off and put away.”
The word hereby is especially useful for people who are issuing proclamations or reading from formal documents. A king might once have declared, “These lands are all hereby claimed in the name of me, the king!” And when you’re on a long family car trip your dad might shout, “I hereby announce that I am in charge of the radio!” Hereby has been used in English since the thirteenth century.
(formal) by means of this“I
hereby declare you man and wife”