Find out how to get the free Man-O-War in COD Mobile Season 7 here.
To unlock Man-O-War you need to complete each task step by step and it can be found in Seasonal event.
1. Kill 80 Enemies with ARs
Use any assault rifle to kill 80 enemies to pass step 1.
This should be able to complete after 6 or 7 match of any gamemode.
2. Kill 50 Enemies with M4LMG
Use M4LMG to kill 50 enemies without any attachments to pass step 2.
Make you did not equip any attachment to your M4LMG.
3. Kill 20 Enemies with Pistol
Go into Multiplayer matches and use J358 or MW11 to kill 20 enemies with it.
It did not count in battle royale match.
4. Kill 40 Enemies with PDW57
Use PDW57 equip with Quickdraw, Foregrip, and Fast mag, and red dot to kill 40 enemies.
Make sure you have 4 attachments on your PDW.
5. Kill 20 Enemies with HS0405
Use HS0405 shotgun and equip with only long barrel and kill 20 enemies to pass step 5.
Don't use more than 1 attachment for your kills won't count.
6. Kill 20 Enemies with M21 EBR
Use M21 EBR sniper rifle and equip with stock attachment to kill 20 enemies to unlock Man-O-War.
After you complete this step you will unlock the common Man-O-War, you can continue or stop at this step.
7. Kill 20 Enemies with Man-O-War
Use the common Man-O-War that you've just unlock without any attachment to kill 20 enemies.
Optic is also counted as attachment, don't use it either.
8. Kill 20 Enemies with Man-O-War (with Attachment)
Now use the Man-O-War equipped with extended mag, quickdraw, foregrip, and red dot sight to kill 20 enemeis.
After you complete this you will unlock a skin version of Man-O-War call Isometric Man-O-War.
Conclusion
In short, To unlock free Man-O-War you need to complete 8 tasks in total in Seasonal event call Lock, Stock, Barrel of COD Mobile Season 7.