Reference an indicator dataset?

From your question title and your question description I perceive you are trying to solve a problem using tools that don’t exist. From your question title: “Reference an indicator dataset”. This is not possible in Thinkorswim. You can do this in other platforms but it is impossible in Thinkorswim.

From your question description I see that you are trying to create an exponential moving average which is based on the RelativeStrength indicator in Thinkorswim. So you want to add a moving average to the RelativeStrength indicator.

In order to accomplish this you must copy the code from the RelativeStrength indicator and use the plot value of that code to compute your moving average.

Here is the full code copied from the RelativeStrength indicator. I have added two inputs for the moving average and I have added one line to plot the moving average.

declare lower;
input CorrelationWithSecurity = "SPX";
input averageType = AverageType.EXPONENTIAL;
input length = 21;
def close2 = close(CorrelationWithSecurity);
plot RS = if close2 == 0 then 0 else close/close2;
RS.setDefaultColor(GetColor(6));
def sr = CompoundValue("historical data" = RS, "visible data" = if isNaN(sr[1]) then RS else sr[1]);
plot SRatio = sr;
SRatio.setDefaultColor(GetColor(5));
plot ma = MovingAverage(averageType, RS, length);

Screenshot below shows the result.