First of all, by default this option is disabled (we like to keep things simple). So if you want to enable the users to move items to other files, the SuperAdmin will have to first set these permissions to "Everyone" (or limit it to Managers and other SuperAdmins). Don't forget to click "Save Changes" at the bottom of the page:

For snaps:
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​For forms:

Once this is set, users can move items in their files. To do so, find the snap/form you would like to move and click the "edit" icon (pencil) to get the edit window:

In the "move to another file" box, you can type the reference of the file you would like to move the snap/form to. Bear in mind that the file that will receive this workflow must be an open file.

Want to move an entire workflow to another file? Read more about it here!