Hi there, this is an old post but perhaps somebody still need the tips.
You need the epic launcher in order to download any asset from the marketplace and there is no versión for linux but fear not, you have some alternatives.
1- Epic launcher via lutris: is a bit slow and can experiment some lag or irresponsiveness from time to time but still is a very solid option.
2- Epic Asset Manager: is a linux app, you can download it in many formats, including flatpak and direct download from github, still has some bugs but is more responsive and fast than Epic Launcher on Lutris.
I use both but in general my first option is Epic Asset Manager.
I hope this is still helpful.
Best Regards