To give more information: 

After we have imported our data to our Secondary storage, Sentinel detects them and suggests that we reindex them. And that's what I do. After reindexing I need to go to Storage -> Events and  Find Data. I manage to find all the newly indexed partition which I select and Restore.  I get the following events into the server0.log. Indexes/partitions are located on our secondary storage:

Tue Nov 12 09:45:02 EET 2024|INFO|ExportEventAssociations-Partition-127289|esecurity.ccs.comp.event.indexedlog.ExportImportEvtAssocThread.run
Starting ExportEventAssociations for partition 127289
Tue Nov 12 09:45:02 EET 2024|INFO|ExportEventAssociations-Partition-127289|esecurity.ccs.comp.event.indexedlog.ExportImportEvtAssocThread.importData
Import directory /var/opt/novell/sentinel/data/eventdata/exported_associations/20230903_D43B9039-ED96-103C-AFF2-005056B90CF4 for partition 20230903_D43B9039-ED96-103C-AFF2-005056B90CF4 (ID=127289) does not exist. Could NOT import event association data.
Tue Nov 12 09:45:02 EET 2024|INFO|ExportEventAssociations-Partition-127289|esecurity.ccs.comp.event.indexedlog.ExportImportEvtAssocThread.run
Completed ExportEventAssociations for partition 127289. Took 8 ms

After restore I get a screen via what I could Apply those newly reindexed and found partitions. Restore data windows tells me that there's Error Importing and info says (this is an example):

Partition Name: 20230711_D43B9039-ED96-103C-B035-005056B90CF4_20240416
Partition Date: 2023 July 11
Event Count: 8
Byte Count: 14.29 KB
Event Association Data Action: Importing event assocation records into database
Action Start Time: 2024 August 27 14:52:20 UTC+3
Action Running Time: 00:04:51.585
Event Association Data in DB: No Records Restored
Event Association Data Exported:YES
Incidents Events Exported: 0
Correlated Events Exported: 0
Incidents Events Imported: 0
Correlated Events Imported: 0
Action End Cause: Import files not found on file system.

After applying selected partitions, they disappear of course, but are not searchable. I don't know if it matters, but reindexed partitions are still mounted during this restore process even though they would have been indexed day or two earlier. 

Regards, Timo

Hi, answering to my self again: problem solvet:

Sentinel says this about Data restoration (storage -> Events after Retention section):

We have made a massive work, built new systems, installed Sentinel and imported many many Teras of log data. That note worked partly during the process. Meaning: only some most recent data (and we upgraded from 8.6) were found by that way. Majority of out logs just were "found" by Reindegin tool (GUI). That was just fine and after reindexin data was ok. I had to add some more logdata after that massive import and this was totally different with info text above. I now know, so one has to import logdata into primary or to secondary, Reindex all the data first and then come here to click Find Data -> it will propably give an error ( Action End Cause: Import files not found on file system.) but nevertheless just Apply and data newly reindexed data is searchable. Note to Opentext: this propably need to be fixed or otherwise informed. I would have save 2 months, but the most important things is that finally found the working process.