Hi @DeepikaR1661877 

Write this script on onChange client script on subcategory field .

function onChange(control, oldValue, newValue, isLoading, isTemplate) {
if (isLoading || isTemplate) {
return;
}

var category = g_form.getValue('category');

if (category == 'Dev' && newValue == 'Test') {
g_form.showFieldMsg('subcategory', 'This is a Test subcategory for Development', 'info');
} else {
g_form.hideFieldMsg('subcategory');
}
}