The ornamental design for a steamer apparatus, as shown and described.
FIG. 1 is a perspective view of a steamer apparatus showing my new design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a right side elevational view thereof;
FIG. 5 is a left side elevational view thereof;
FIG. 6 is a top view thereof; and,
FIG. 7 is a bottom view thereof.
The broken lines shown in the drawings are provided for the purpose of illustrating portions of the steamer apparatus that form no part of the claimed design.