Tower Controller reported issuing an instruction to fly runway heading prior to instructing the aircraft to execute the published missed approach; which was a violation of the MVA.

Narrative

I was working Local Control 1; 2; helicopters; and Ground Control combined; approximately around XA:00. The weather was extremely poor; less than 1/4 SM visibility; mist; and a vertical visibility variable between 100 - 200. The [Runway] XXR RVR was variable between 600 - 1000. The field could not be seen from the Tower. Aircraft X was inbound on the ILS-Z and was given the RVR. On very short final; they decided to initiate a go-around. I issued runway heading and thereafter; an instruction to execute the published missed approach. Issuing a heading is a violation of the MVA.The reason why I gave runway heading is because I was informed of an event in the past where another jet on a 2-mile final for the ILS-Z [Runway] XXR initiated a go-around but had the wrong chart pulled up and started the climbing left turn prior to the ZZZ 1.5 DME. I had this event in my head when issuing the runway heading instruction just to ensure they got to the point to execute the published missed. I spoke with our facility Quality Assurance Evaluator and was told that this was a violation of the MVA and in the future to just simply instruct the aircraft to execute the publish missed approach as the procedure has the crossing restriction on it; or to say fly to the missed approach point and then execute the published missed approach. I explained my reasoning to the Evaluator and he understood; but in the future; I will have no problems issuing only the published missed approach.