If you were active during that time you would have received some merits as they were airdropped based on your rank at that time which you can know from the merit thread linked above.

For every good post you make or any member thinks it's helpful post he/she can send you merits for the same and there are merit sources also to help you around.But if you feel you have made good contributions still your posts have not been noticed you can share them here : [self-moderated] Report unmerited good posts to Merit Source but you don't have any at this time so you need to work on making some posts first of all.

You can send merits as a newbie also but for that you need to earn them first of all but you need only one merit to rank up to junior rank as you have enough activity for the same but only lag merits.So you can gain them by above mentioned ways by increasing your knowledge and contributing more to forum.