We are not able to view and assist with moderation issues on your Realm directly. However, we do have a guide to help you with some of the Realm moderation options built-in. You can access these by clicking the Edit Realm Icon next to your Realm in the server list. 
 
1. Close the Realm - This prevents anyone from joining your Realm until you open it again. 
2. Set "Guest" permissions by default - Invitees that join your Realm will be unable to make any changes to the world, such as breaking blocks, griefing, or making other undesirable changes. 
3. Restore from a previous backup - You may be able to roll back to a previous backup before any undesired changes were made. 
 
Realms also uses an invitation-only system that helps prevent unauthorized access. Access and per-player permissions can be managed through your Realms admin settings. 
 
For more information, you can visit our Realms Admin Options articles.  

For Minecraft: Java Edition, see What Admin Options are Available 

For Minecraft Bedrock Edition, see Realms Plus Admin Options