From the within the Audit Log, click on the filter icon on the right hand side:

This will reveal the filter panel:

Using the various filters available here you can search and pinpoint exact activity as required. 

For example, should you wish to find out who made changes to a user record, you could apply the filters as shown below:

This would then filter the audit log accordingly, and you can click on the item in the table to view more information. E.g. the below screenshot shows us that the user "Mike Jones" was updated on the 16th April 2019 at 08:04 by the superadmin. Clicking on this reveals the change made was to the Forename, from "Michael" to "Mike".

To clear any filters, click back on the filter icon, which will show red when filters are applied...

...and click, Clear Filters.