To restore a database snapshot you will need to use the 'tdbutil' utility which will have been installed with the server (typically 'Program Files\PureCM\Server').
Open a command prompt in the server executables directory.
Type 'tdbutil import <snapshot> <database>'. For example if you have a repository called 'Test1'. The snapshot file will be called 'r_Test1_1.xml.gz'. In this instance you would type 'tdbutil import r_Test1.xml.gz r_Test1'. This will create the corresponding r_Test1.tdf, r_Test1.tbf, r_Test1.tlf and r_Test1.tpf files. These files should then be copied into the PureCM data directory (typically PureCM\data).