The first condition to achieve the Weapon Master Achievement Title is that you play a Classic Match.
The second Condition is you need to be above Platinum Tier and above and also play in the same Server wherein you have the Platinum Tier.
The third Condition is that you need to complete all the below tasks in one single match.

*Note: You will have to knockout a player with the same weapon and kill with the same weapon. 

Thank you for supporting PLAYERUNKNOWN'S BATTLEGROUNDS MOBILE!
Kindly Reminder: For public policy matters, please send an email to policy@proximabeta.com