Short answer. File an affidavit of your title or right to possession, stating the grounds, and serve it on the sheriff while he still holds the property, with a copy to the applicant. The sheriff is then not bound to keep or deliver it unless the applicant posts an indemnity bond.
What the law says
makes an affidavit of his title thereto, or right to the possession thereof, stating the grounds therefor, and serves such affidavit upon the sheriff while the latter has possession of the property and a copy thereof upon the applicant
Rule 60, Section 7 — Proceedings where property claimed by third person. Read the full provision →
The remedy is an affidavit, and it is time-sensitive
The rule gives a person who is not the defendant a specific route, and it is not a motion in a case you are not party to. It is an affidavit of your title to the property, or of your right to possess it, stating the grounds. Two service requirements go with it: on the sheriff while the latter has possession of the property, and a copy on the applicant. The timing element is built into the rule itself — the affidavit is designed to reach the sheriff while the property is still in his hands.
What the affidavit actually accomplishes
It does not order the property returned to you. Its effect is that the sheriff shall not be bound to keep the property under replevin or deliver it to the applicant unless the applicant, on the sheriff's demand, files a court-approved bond to indemnify you. So the affidavit shifts the burden: the person who obtained the writ must now put up security if he wants the seizure to continue. It converts a dispute you were shut out of into one where your exposure is backed by something.
The size of the bond, and who fixes it
The rule requires the indemnity bond to be in a sum not less than the value of the property under replevin. It then addresses the obvious dispute — value is exactly what parties disagree about — by providing that in case of disagreement as to that value, the court shall determine it. That is worth knowing, because it means you are not obliged to accept the applicant's figure. Once the bond is filed, the rule also provides that the sheriff is not liable in damages to the third-party claimant for the taking or keeping.
Your underlying claim survives either way
The affidavit procedure is not your only avenue and does not replace your ownership claim. The rule states expressly that nothing in it prevents such a claimant or any third person from vindicating his claim to the property. There is also a time limit that matters if you later want to recover on the bond, so this is not a situation to leave sitting. Get the affidavit and your proof of ownership to a lawyer quickly, while the sheriff still holds the property.