The ornamental design for a cover for upperportion of a chair, as shown and described.
FIG. 1 is a left rear perspective view of the present invention; and
FIG. 2 is a rear view of the present invention; and
FIG. 3 is a front view of the present invention; and
FIG. 4 is a left side view of the present invention; and,
FIG. 5 is a right side view of the present invention.
The broken lines showing of parts of the drawings is included for the purpose of illustrating use and environment and forms no part of the claimed design.