Hi Krisse,
Typically if your web service is running under IIS you would have logging enabled in IIS and could examine the log files under C:\inetpub\logs\LogFiles\W3SVC1 by default. Have you checked there? You may open the files in Notepad.
You can look in IIS Manager, select your server in left pane, then in right pane double-click on Logging icon to see logging configuration.Another potential option is NSG flow logs, however, you would've needed to have this configured before the incident. You can't go back in time to see flow logs if the feature wasn't enabled.
Windows Defender Firewall with Advanced Security (wf.msc) has logging ability as well, however, by default it isn't going to log successful connections so this is another case where you would've had to have it configured to log beforehand.
Please click Accept Answer and upvote if the above was helpful. If something is unclear add a comment.
Thanks.
-TP