Add URL Prefix to requests using nginx or rails - ruby-on-rails

Question

I'm trying to understand the best way to redirect all traffic for https://app.company.com/ to https://app.company.com/app
app.company.com is a rails 4.2 server which uses nginx to serve static assets and unicorn to handle the rails requests.
Should this redirect happen in nginx or rails?
Back story:
A few years ago I supported some rails apps that were installed on the intranet using URL Prefixing, like:
https://company.com/app1/
https://company.com/app2/
https://company.com/app3/
company.com ran an nginx server which routed traffic to each app server based on the url prefix.
Each app server runs nginx to serve static assets and unicorn as the rails server.
Recently a decision was made to hand management of the company.com server over to the parent company. As a result, a decision was made to route to each rails server by DNS using subdomains in place of nginx rules.
For now apps will be accessed using:
https://app1.company.com/app1/
https://app2.company.com/app2/
https://app3.company.com/app3/
Individual app servers are largely unchanged. They still run nginx and unicorn.
My main issue is understanding the best way to push traffic for the root to the url prefix
https://app1.company.com/ --> https://app1.company.com/app1/
The root route without the url prefix never reached the rails servers before.
UPDATE
Here is my nginx config file with original enhancement proposed by Vashed's answer.
I'm now curious if there is a refinement to this which would allow my config file to be independent of the server name like it was before.
upstream unicorn {
server unix:/tmp/unicorn.app1.sock fail_timeout=0;
}
server {
listen 80 deferred;
# ADDED THIS LOCATION BLOCK PER VASFED'S ANSWER
location = / {
rewrite ^ https://app1.company.com/app1;
}
location /app1/assets {
alias /var/www/application/current/public/app1/assets;
}
# Serve file uploads from nginx
location /app1/system {
alias /var/www/application/current/public/app1/system;
}
try_files $uri $uri/ #unicorn;
location #unicorn {
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header Host $http_host;
proxy_redirect off;
proxy_pass http://unicorn;
}
client_max_body_size 1G;
keepalive_timeout 10;
}

Answer 1

You can issue a redirect using nginx:
server{
server_name app1.company.com;
listen 443 ssl;
# other setup
location = / {
rewrite ^ https://app1.company.com/app1/;
}
location / {
# as before
}
}