If you right click the frame, you open the context menu:
Its functions match those of text frames except that you cannot assign the pagination frame to an XML node, the content can also be formatted like normal text.
The pagination starts with 1 by default. If you need the pagination to begin with another number, you can achieve this by entering the desired number into the field Alternate page number in the page’s properties:
As you see, you need to check the check box first to activate the entry field for the alternate page number. Double click the entry field to make it editable and enter the number that you want to start the pagination with. Find more information about customized page numbering in the chapter Page.