After reaching the destination, he dismounted from his bike to take a break.

dismounted 是动词 dismount 的过去式形式。dismount 由前缀 dis-（表示"离开、去除"）和 mount（"骑上、安装"）组成，字面意思是"从骑乘物上下来"，特指"从自行车/马背等交通工具上下来"的动作。