The ornamental design for swivel tool head, as shown and described.
FIG. 1 is a perspective view of swivel tool head showing my new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof,;
FIG. 4 is a left view thereof;
FIG. 5 is a right view thereof;
FIG. 6 is a top view thereof; and,
FIG. 7 is a bottom view thereof.
The broken lines depict portions of the swivel tool head that form no part of the claim. The dot-dash-dot lines represent a boundary of the claim and form no part of the clam.