How can i use combobox as level selection ?,How can i use combobox umg as levels selection ?,How can i open levels with combobox?

So i want to use combobox as level selection so my level list doesn’t fill up my screen,
well iv’e tried but when i tested it but an error comes up.

i did this OnSelectionChange-----Set---------------------StringToName--------OpenLevel

and that open level i attached button to it
and that mapName should be below that set