repair concrete

Was preparing the area to have new windows installed and when removing the skirting board noticed a corner of the concrete floor missing, any suggestions on how to fix it? Do plan to have a tredboard wall to wall woth skirting board on top.

We have removed the flat porch roof of our Laing Easi-Form house which has left the concrete exposed. The concrete needs filling first then we will render and paint over the top. Searching online I can find loads of concrete repair mortar or epoxy but they all seem to be for floors. The Watco...