Unfortunately, there is no such way you can get free diamonds as it would be unfair to other players. However, you can get some free items in gold such as skin, emotes, fashion, characters, other collectables etc.
There are some ways to get free items:
Level up your account to get free characters.
Use Free Fire coupons to save money.
Get gifts by completing free Fire Max Pass assignments and earning badges (new Fire Pass every month).
Earn Rank Tokens by playing rank, which may be redeemed for free goodies in the Exchange Store.
Take part in timed in-game events for free rewards (collection items, tools, skins, fashion, and characters, among other things).
In the Store, some characters can be acquired with gold.
Some Luck Royals may award you with free spins or gold as you spin (Gold Royale).
7. Join a guild, perform guild quests, and earn Guild Tokens to use in the Exchange Store to get gifts.