Lewis structure of ammonium ion
Coordinate covalent bonds do not exist.  They are all plain old covalent bonds.  We use "coordinate covalent bonds" as a means of counting electrons from atoms that go into bonds; here nitrogen contributes five electrons to four bonds so we figure that the nitrogen must have contributed two electrons to one of the bonds.  But the actual bonds formed between the nitrogen and each hydrogen atom are all alike.  Ammonium ion has the same tetrahedral structure as methane, and for methane we do not need coordinate covalent bonds to count the electrons.