What Should One Do If He Did Teshuva and Stumbled With the Same Aveirah Once Again

The Orchos Tzadikim (Sha’ar 26) writes, that if one did teshuva on a particular aveirah, and then he stumbled a second time, and even a third, he can still do teshuva. However, one who is doing teshuva a second time, must do a more sincere and severe teshuva.