Yes, you can revert an item record to an earlier version. When you open an item in Ketryx from the All Items screen, you can see its item record history on the right-hand-side menu, as shown below:

Clicking on an earlier version of the record and selecting Restore as current will revert the record to an earlier version, as shown below:

Note that restoring a record will not "reverse" the record history. Restoring to a previous version of the record will create a new revision of the record that is identical to the targeted restore version. Ketryx will propagate the change into Jira if the source record is a Jira record. 

If the Restore as current option does not appear, it may be because Item record restoration has been turned off (it is allowed by default). To toggle this setting, see https://docs.ketryx.com/reference/advanced-settings#allow-item-restoring