How do i resolve this issue of my vivo hotspot turning off in its own? I can't even see any additional settings
All you can do is to keep a device connected. The device turns off the Hotspot when it sees no device using it for over 2 minutes.
This is certainly a very strict timeframe. Anyhow, the setting to automatically close Hotspot is baked into the system and as such, it will not be possible to override it.