We do not have any pair testing feature out-of-the-box, but I can recommend some customization to the settings that come close to achieve the purpose here.
1. Create a custom field named 'Reviewer' in your executions.
You can have dropdown or a text field for reviewer.
2. Since we already track who is execution test cases, you already got that on file.
3. When you assign an execution (for pair testing), assign the person normally like you would do in Test Collab and fill in the custom field 'Reviewer' with your desired team member's name.
One small limitation here is, reviewer won't be informed when you assign him, he'll have to be manually informed about the task.
That's it - now you know who executed and who reviewed the test.