restore database '/xx/xx/dm.ini' from backupset '/xx/xx/xx' （增备目录） with backupdir '/xx/xx/xx' （全备目录） ;
增备还原是这样操作的，需要带上全备和增备目录，修改后再试试

首先check下备份，
RMAN> check backupset '/opt/dm/bak/dmdb_full_bak_tuoji'
RMAN> check backupset '/opt/dm/arch'

还原范例，
RMAN> restore database '/opt/dm/data/DAMENG/dm.ini' from backupset '/opt/dm/bak/dmdb_full_bak_tuoji';
RMAN> recover database '/opt/dm/data/DAMENG/dm.ini' from backupset '/opt/dm/bak/dmdb_full_bak_tuoji';
RMAN> recover database '/opt/dm/data/DAMENG/dm.ini' with archivedir '/opt/dm/arch'; --如果需要恢复归档文件就加上这一行命令，日志要从全备开始的。
RMAN> recover database '/opt/dm/data/DAMENG/dm.ini' update db_magic;

这个应该不是 disk 备份的吧。是通过第三方备份软件，可以问问 命令是不是 少参数了