Walls – How to drain a small retaining wall built for flowers

I have one of these in front of my house. From what I could see the previous owner was not very smart when he built this, it is sloped toward the house and moreover this is on the north side of the house, it gets sun light for a 1-2 hours in the afternoon so not only that it is not very practical for flowers (he put some shrubs there that are struggling to survive) but it seems to retain water (I can see some moss building up there)

Question: after I slope this correctly by adding more dirt how do I drain this? Do I need to drain it at the upper level or should I build something that is dug in and drain it at the base level (the grass level in the picture)

Thanks lot