After having made the changes in your Studio template, the big thing is to click "Save and publish" before going into Creative Manager.
I assume you have now clicked "Save and publish" in Studio; otherwise, you are a true rebel that no law can hold back, and these next few steps will need you to do some Jedi mind games. Start by going into your Campaign overview and;
Go to the Creative Set your need to update, where you will see a yellow top line indicating a pending design update
Hover your Creative set and click the 3 little dots
Click on "Update design"
In the update view, you will be able to go through your formats on your left hand to see a before and after, as well as formats added or deleted. Then, when you have checked that the updates are correct:
Click on the new formats under "Template Updates" you want added to the Creative set
Choose "ignore for now" or "Accept Updates" in the bottom right corner
Now your Creative set is updated and ready to be exported. If you are one of the lucky ones who host through Zuuvi, remember to click 'Publish' on your Creative Set so the changes will be pushed to the live creatives. 🤠