You could lower the weight, as mentioned, by ~20% and do the last set as a AMRAP (As Many Reps As Possible) set. This will let you work in a higher rep range, and maybe get back to your previous weights doing more reps on the last set.
You could switch to another rep scheme with the same total reps per workout, but less reps per set e.g.: 6x4 or 8x3. This will let you continue to add weight.
You could add in some accessory work.
You could eat more and gain some weight.
You could do another program entirely.