The question is not clear. An answer requires to know the contents of the cell elements and it depends on what you want to do with it.
Please post only one question per problem. See https://www.mathworks.com/matlabcentral/answers/382725-how-to-convert-a-cell-to-a-string . Here you did not tell us also, what the contents of the cell is and what you want to do with it.