What to do with long waiting time ?

[theteer]

I have a Ultimate Managed WordPress Websites hosting plan and optimised my wordpress as far as I could.

When I am checking in Google PageSpeed Insights I am getting the result bellow,

So Checked in Gt Matrix and I could identiy the slow loading is because of Waiting time, sharing the results bellow

 Now my question is, how to reduce waiting time of Teer ?