I claim the ornamental design for a cover for a car seat arm support, as shown and described.
FIG. 1 is first perspective view of the cover for a car seat arm support in a closed condition, showing my new design;
FIG. 2 is a second perspective view thereof;
FIG. 3 is a front view of FIG. 1;
FIG. 4 is a top view of FIG. 1;
FIG. 5 is a left side view of FIG. 1;
FIG. 6 is a right side view of FIG. 1;
FIG. 7 is a front view of FIG. 1, with the straps shown in an extended full length condition;
FIG. 8 is an inside view of FIG. 1 in an unrolled opened arrangement;
FIG. 9 is an outside view of FIG. 1 in unrolled opened arrangement; and,
FIG. 10 is the cover for a car seat arm support shown in use.
The broken line showing of a car seat arm support is included for the purpose of illustrating environmental structure and forms no part of the claimed design.