Help! Is there a way to change the concatenate from a comma to a hard return?

I have a trigger to copy all the items from a sub-table ('Item Desc" into a multiline field ('LongDescription'),

LongDescription := concat(Items.'Item Desc.');

but it copies the items with a comma between them. Is there any way to change this to a hard return (paragraph mark)?

I'm been trying to solve this with a loop but I'm a newbie and would love any help. Thanks