what if I failed in 12th boards but pass the retest am I eligible for neet? or is this valid for neet?

You must have completed your 10+2 atleast by the time of counselling. If you have failed your Board exams then you can appear for Improvement exam or Retest atleast before July 26th, then you can appear for NEET. So you'll be treated as the Students who are appearing for their 12th exams. But in case your retests are after July 26th then you cannot appear for NEET.

Hey there

The eligibility criteria of NEET is that candidates must have passed 10+2 or equivalent with Physics, Chemistry, Biology/Biotechnology and English as core subjects from a recognized board. Candidates who are appearing for the class 12 or equivalent exam are also eligible to apply for NEET 2020. So if you fail in your board exam then you are not eligible.

Check the link

https://www.google.com/url?sa=t&source=web&rct=j&url=https://medicine.careers360.com/articles/neet-eligibility-criteria/amp&ved=2ahUKEwiTj6by37zpAhWQ8XMBHeK2CVsQFjAAegQIBBAB&usg=AOvVaw3J48XLYjRlxkl5RSraYMod&ampcf=1

Good luck