Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
I presume that you have Brother GX-6750 typewriter, and the daisywheel:
has fallen off its mounting.
First see if it is broken in any obvious way - any 'spokes' missing.
Then see if the mounting hub is broken or cracked.
If spokes are missing or the mounting hub broken or cracked, a new daisywheel will be needed. The above-cited is only one example - there are other types available than Brougham. Let me know what you need in that case, and I will refer you to a good source for a replacement.
The daisywheel, if still OK, simply needs to be re-mounted on its hub or mounting.
Open the top of the printer, remove the ribbon cartridge and set it aside for the moment. Look for a small metal spindle, of the right size to fit into the center hole of the daisywheel. Place the daisywheel onto that spindle, with the numbers-and-letters side toward the paper or where the paper will be or toward the platen cylinder. Press the daisywheel firmly into place until it is obviously held there and does not wobble at a touch.
Then put the ribbon cartridge back into place, and close the typewriter, and resume typing after a brief pause (and any necessary adjustments to the paper, of course.)
If you need a guide with illustrations, here is a source for your model of typewriter's user guide, free of charge, from Brother's website:
Let me know how it goes, please... or if you need further assistance.