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 figure drawings depict portions of the steamer apparatus that form no part of the claimed design. The dot dash lines in the figure drawings indicate the bounds of the claimed subject matter and forms no part thereof.