Repopulating PostgreSQL database with data directory from another database Instance
Assumptions

I'm assuming you have two instances each one with a different data directory but with the same schema for the same version of postgres installed.
I'm also assuming when the server starts is using your newly created, possibly empty, instance

What to do

You should try to start a new instance of the server pointing to your backup data directory...
Somenthing like

pg_ctl -D /path/to/backup/dir -l /path/to/log start -o "-p 5433"


If this works, your backup instance is running on port 5433.
Check if everything is in place and the data is consistent.

If so then you could simply make arrangements for your server to always start pointing to your backup directory and safely delete your newly created data directory.