Go to https://learn.microsoft.com/en-us/dotnet/core/install/linux-scripted-manual#scripted-install
Download https://dot.net/v1/dotnet-install.sh
Run this :
./dotnet-install.sh --channel 8.0
export DOTNET_ROOT=$HOME/.dotnet >> ~/.bashrc
export PATH=$PATH:$HOME/.dotnet:$HOME/.dotnet/tools >> ~/.bashrc