Mo. Rev. Stat. § 513.480

Whenever an execution shall be levied upon the real estate of any person, of which such homestead may be a part, or upon such part of any homestead as may be in excess of the limitation of the value thereof created in section 513.475, such person shall have the right to designate and choose the part thereof to which the exemption created in section 513.475 shall apply, not exceeding the limited value; and upon such designation and choice, or in case of a refusal to designate or choose, the sheriff levying the execution shall appoint three disinterested appraisers, who shall, first being sworn to a faithful discharge of their duties, fix the location and boundaries of such homestead, and the sheriff shall then proceed with the levy of such execution upon the residue of such real estate as in other cases; and such proceedings in respect to the homestead shall be stated in the return upon such execution.