You have appeared for 12 th class Bihar Board initially in the year 2018 and again in view of your better performance , you appeared again in 2019 for the same class from Bihar Board. However, you have not indicated how you have performed your examination in 2019. There might be two cases in such an attempt. If your scores are less in 2019, the same scores will be treated as valid and so is the case of your higher marks, it would be treated as your final result.
In all the situations, results of 2019 would be final.
However in all the cases, you need to show the results of both the year - 2018 & 2019 specifying the details of marks of both the years if you appeared in some of papers for improvement. If you have appeared for the all the papers in the next year, you need not mention the results of the two consecutive years. In that case, your scorings of 2019, would be reckoned as your final result.