Regular past-tense formation rule: The past-tense morpheme '-ed' has three different allomorphs, such as [t] [d] and [Id]
1. help. look, kiss, wish ==> [t]
Those ended with a voiceless sound(except for 't' and 'd'), read as helpt
2. love, cuddle, kill, lie ==> [d]
Those ended with a voiced sound, read as loved, killd
3. state, wound ==> [Id]
Those ended with a voiced sound, read as statId, woundId
Does that help?