Thanks for the reply.
What you mean for this sentence. I actually followed the steps you have mentioned, but right now, If I type ./launcher rebuild app, after a while I am getting another error saying that " [2019-07-02T11:51:07.931930 #16] INFO – : > cd /var/www/discourse && gem update bundler
ERROR: While executing gem … (Gem::RemoteFetcher::UnknownHostError)
timed out (https://rubygems.org/specs.4.8.gz)"