What is the role of 在 in the sentence 当我有错误在帮我纠正就行了
It may be a mistake. It should be 当我有错误再帮我纠正就行了 or the complete version 当我有错误的时候再帮我纠正就行了 .
There is no relationship between 再 and 时 . There will always be a 时 in the meaning of this sentence even though you can omit it.
Because  of 就行了 ; there will always be a 再 in the meaning of this sentence.
After you remove 就行了. 再 makes this sentence sounds like &quot;not now; correct me untill I made a mistake&quot;. If you remove 再,  this sentence will become a imperative sentence like an order.