Thank-you for your post.
ELIS versions have 4 numbers, the first 3 are the Moodle version it's released for and the fourth is the ELIS version, for that Moodle release, so I assume you are referring to ELIS 2.8.6.0 (which should be run on Moodle >= 2.8.6).
We cannot recommend modifying database table values directly, and, there is no way to reprocess ETL data from a timestamp in the past. However, the ETL data maybe reprocessed if the table was restored.
Please note that in ELIS versions >= 2.8.5.2 the ETL data was updated to be generated from the new Moodle {logstore_standard_log} table - previous versions used the old Moodle {log} table, and the ELISCore ETL required that legacy logging be enabled.
We currently have an issue (ELIS-9209) to address an ELISCore ETL problem, not collecting data, with the latest ELIS 2.8.7.0 and ELIS 2.7.9.0 releases (may affect older ELIS versions too, but does not appear to affect ELIS 2.9.1.0); which will be fixed in a subsequent ELIS release.