Hi Raquel
I installed a copy of the Gym site locally and see that you won't be able to re-use the existing fields, you need to create a new group for your new post type.
You will have created a new post type (I don't know your project, let's say it is "Dentists"), and you want to use the same opening hours custom fields with your dentist post type.
Ordinarily you could edit the existing custom field group for Gyms and make the same fields available to your dentist post type (and no longer available to gyms, if you will be deleting that post type), so the field names and slugs etc. would be just the same as before.
But, those opening hour fields are implemented using repeatable field groups (screenshot), and it is a limitation arising from how they are implemented that they are tied to a specific post type, so you cannot re-use the existing fields for another post type, you will have to recreate them.
So make a new custom field group for dentists, adding the fields you need, including reproducing how the opening hour fields are set up in the field group for gyms. You will run into the problem that the slugs for the fields (such as "day-of-the-week") are already used, and you will need to use different ones.
You should then be able to publish your dentist posts with values for the custom fields, including opening hours.
Now, to the main point of your question.
You will have made a template for dentists, and want to display the opening hours.
So you will need to insert a View block, and you will be creating a new View.
After choosing the output style, you will choose the content selection, and you should find your new repeatable field group for opening hours available to choose.
You would then design the output of the View to include the required fields. If you examine the existing View in the Gym template you'll see that in the output section it uses a container block with a column block inside with 2 columns, with the first showing the day and the second showing the hours, each coming from the repeatable field group.
You may find the Getting Started guide for using Views to display lists of content helpful, although it doesn't refer specifically to displaying repeatable field groups: https://toolset.com/documentation/getting-started-with-toolset/create-and-display-custom-lists-of-content/