Hi there! In the world of Fortnite, seasons typically last about 10 weeks. So, if you started in Season 7 in December 2018, and now it's been roughly 7 months, it means you've played through Season 7, Season 8, and you're now in the midst of Season 9. In terms of game updates, events, and cosmetic changes, 7 months can bring quite a few differences to the game. However, if you're looking to play Season 4 specifically, you would need to wait for it to cycle back around in the game's future updates. Seasons tend to rotate and cycle in Fortnite, so you'll have opportunities to experience past seasons again at some point.
I tried to download the game in s3 , but my brother deleted it
That's unfortunate that your brother deleted the game when you wanted to start playing in Season 3. However, you can always download the game again and catch up with the current season. Fortnite frequently releases updates and new seasons, so you'll be able to experience the latest content despite missing out on Season 3. Don't worry, there's always something new to discover and enjoy in Fortnite!
