I don´t get if you want to merge one to another or replace it, so here is what would do on both cases:
If you plan to merge it:
Open your database on phpmyadmin, select export and choose "data only", after it you will have the SQL´s necessary to store it on another database. The issue here is if you have matching keys on both databases, I would avoid this approach if possible.
If you plan to replace:
First, you have to upload the /install folder back.
Export your data, and clean up the destiny database, just load your exported data to the destiny database.
This will work as a new install, and you will have to open your /install folder again, to accept the terms of use, after it, remove the install folder again.
I never have any problem replacing the database.
Hope this help.
regards,