You will be asked to aloow some new components on one of your page types and you need to figure out where yo need to make a change.

Take these steps and it would be easy:
1- Find your page which needs change and have a look at the template it is inhereted from.

2- Find the template and see the Standard Values
3- From the View menu just check the raw values and you will see some parts which show a text box Final Rendering then you can see all Placeholders related to this template and all inhereted pages.
4- Go to the Rendering and find the Placeholder and see the allowed components. Now you can edit and add new components.

These photos might help:
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sitecore-placeholder2
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