You should stir the choc if you m/wave it and as above use a lower setting is probably better unless youhave done this regularly and can second guess the melting. A bowl over a pan of hot water is really the best method. Takes a couple of minutes but he results are going to be predictable.
As it was scorched it can't be used as the flavour will be mucked up - even adding pure oil of coca butter won't help.
There is a lot of fat in choc, and one remedy if the choc thickens too much - cos of water getting into it - add a little pure white fat - not butter - and this will thin the choc a bit. If its still too thick - stir in some cream and you have a great choc sauce.
Steam will 'break down' the choc, as this introduces water which is a no-no.