Question

when I reached there,he (just leave) ...correct verb form

Answer 1

Hey mate ☺

When I reached there, he just left

Hope it helps you ☺✌✌

Answer 2

Your question: When I reached there, he (Just leave). Here you have asked to correct the verb form.

Here the verb in the bracket is leave where the sentence is already in past tense the second verb(leave) in the sentence has to be changed to past tense.

hence the answer to your question is "when I reached there, he just left".

Now in the answer, both the verbs in the sentence were changed to past tense.