FLR(HRO) Need help with Documents guidelines.

I am applying for FLR(HRO) extension under 10 year rules.

I was given 2.5 years Leave to remain outside the rules based on PRIVATE LIFE.

I need help with what documents to attach when sending the application for extension?

I need to submit the application by the end of August 2018.

Some guidance would be really appreciated.

Thanks