Hey @michalgarvey
Welcome to the community and congrats on your first post! Happy to help with your A/B test.
You can identify which customers received a certain variation of your A/B test by creating a segment. To create a segment on which profiles received which variation, please use the following condition:
- What Someone has done > Received Email > At least once, over all time > Where Message Variation > equals (VARIATION MESSAGE) see the following example for how this should look:

You would then repeat this for the other variation in another segment.
Hope this helps, and thanks again for being part of the Klaviyo community!