NO, you don't need to go back to week 1, rerun run 1 of week 6 perhaps 3 times over 7 days, on Wednesday, Friday and Monday or whatever days suits you.
Only if you have not been running for a much longer time, then you would have to go back to the first week.
If you read the guide to the plan healthunlocked.com/couchto5... it advises that you lose next to no discernible condition in the first two weeks of non running..... pick up where you left off.
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