Open the file where the text styles are that you want to transfer.
Open the file you want to transfer them to.
In the resource browser, choose the file with the text styles, select the text styles you want, right click and choose import.
Try making a file with the text styles you use then save it in the favorites folder. When you navigate to that favorites files, select the text styles you want then right click and choose import. You can also add more text styles to the file as you need them.
Alternatively, if you have a template file, create the text styles within the template file so the text styles you want are already in your document then resave it as a template. You can always add more text styles there as well and resave as template.