The b2evolution files are present on your server, but it seems the database is not yet set up as expected.
For more information, please visit our Getting Stated / Installation Guide.
This is b2evolution version 6.8.6-stable.
You cannot use the application before you finish configuration and installation.
Please use the installer to finish your configuration/installation now.
On most installations, the installer should be here (but I can't be sure since I have no config info available! :P)