Have a read of the policy from the link I posted.
The rules are different for proctored exams, non-proctored exams, and beta exams.
For proctored exams, like the VCP6-DCV Delta exam you asked about:
You can attempt it multiple times til you pass it, and you have to leave at least 7 days between attempts - just bear in mind you will need to pay each time so it's probably better to wait a little longer and be fully prepared than to try it again and again.
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