Move the selection below the guide line

Perhaps something like this?

/*
Move Selection Top to Horizontal Guide Coordinate.jsx
v1.0 - 20th April 2023, Stephen Marsh
https://community.adobe.com/t5/photoshop-ecosystem-discussions/move-the-selection-below-the-guide-line/td-p/13738648
*/

#target photoshop

var savedRuler = app.preferences.rulerUnits;
app.preferences.rulerUnits = Units.PIXELS;
if (activeDocument.guides.length === 1 && activeDocument.guides[0].direction == Direction.HORIZONTAL) {
    var hGuidePos = activeDocument.guides[0].coordinate.value;
    try {
        activeDocument.selection.bounds;
        var selTop = activeDocument.selection.bounds[1].value;
        var vMove = selTop - hGuidePos;
        moveSel(0, -vMove);
    } catch (e) {
        alert("There is no active selection!");
    }
} else {
    alert("There are multiple guides and or the guide is vertical!");
}
app.preferences.rulerUnits = savedRuler;

function moveSel(horizontal, vertical) {
    var s2t = function (s) {
        return app.stringIDToTypeID(s);
    };
    var descriptor = new ActionDescriptor();
    var descriptor2 = new ActionDescriptor();
    var reference = new ActionReference();
    reference.putProperty(s2t("channel"), s2t("selection"));
    descriptor.putReference(s2t("null"), reference);
    descriptor2.putUnitDouble(s2t("horizontal"), s2t("pixelsUnit"), horizontal);
    descriptor2.putUnitDouble(s2t("vertical"), s2t("pixelsUnit"), vertical);
    descriptor.putObject(s2t("to"), s2t("offset"), descriptor2);
    executeAction(s2t("move"), descriptor, DialogModes.NO);
}