You don’t have to create a new campaign, you can simply pause or remove the wrong-ratio video from your ad set, so only the correct ratio version runs.
Here’s how you can do it depending on how you set up the split test:
If it’s a normal ad set with multiple creatives (no formal A/B test tool):
Go into your campaign → ad set → ads.
Find the ad with the wrong-ratio video.
Click the green toggle to turn it off (pause it).
Keep the correct-ratio ad active — it will get 100% of the spend.
If you used Meta’s built-in A/B testing tool:
You can’t directly “swap” creatives mid-test.
You either end the test early and keep the winning creative (the correct ratio), or
Duplicate the winning creative into a fresh ad set/campaign and pause the old one.
Pro tip for future tests:
If you just want to swap assets without starting from scratch, use the “Edit Ad” → “Change Media” option. It keeps the ad ID (and learning data) intact, which helps performance stay stable.