Tenn. R. Civ. P. 15.03
Whenever the claim or defense asserted in the amended pleadings arose out of the conduct, transaction or occurrence set forth or attempted to be set forth in the original pleading, the amendment relates back to the date of the original pleading. An amendment changing the party or the naming of the party by or against whom a claim is asserted relates back if the foregoing provision is satisfied and if, within the period provided by law for commencing an action or within 120 days after commencement of the action, the party to be brought in by amendment (1) has received such notice of the institution of the action that the party will not be prejudiced in maintaining a defense on the merits, and (2) knew or should have known that, but for a mistake concerning the identity of the proper party, the action would have been brought against the party.
Tenn. R. Civ. P. 15.03