This is the most popular method, you get a free name card from PUBG.  You can collect this ID card by completing the 10th mission in the Progressive Mission section.

You can get unlimited ID cards by participating in crew challenges.  All you have to do is participate in crew challenges and earn crew points.  Once you have earned 200 crew points you can go to the crew section and then tap on the shop.

If you have purchased a Royal Pass for Season 6 you can submit a free ID card.  It is only for Royal Pass 6 users, apart from free ID cards you also get Royal Pass Mission Cards.  These cards can be used to complete missions.

  After launching PUBG Mobile, you will find an upgrade event banner in the bottom right.