The phrase 'holding reins' usually suggests an element of control or power. Antonyms for 'holding reins' would therefore be words that indicate a lack of control or power. Some antonyms that come to mind are surrendering, yielding, releasing, letting go, giving up, and abdicating control. Surrendering implies a willingness to submit or admit defeat. Yielding suggests a temporary holding back or bending to another's demands. Releasing implies a letting go of something restrains, while letting go suggests a conscious decision to stop holding onto something. Giving up implies a loss of hope or conceding defeat, while abdicating control suggests a relinquishing of authority.