Create and edit drawing tools from chart study

I changed the title of your question to include the context of what you are trying to accomplish. The original title you entered missed some important details and I know that many users of Thinkorswim are searching for this very solution. The title I have chosen should make it much easier for other traders to locate this question when searching for this solution.

Now for the bad news. This is totally impossible to do on the current version of Thinkorswim. We can do this on many other trading platforms. However Thinkorswim does not provide any methods for creating or editing drawing tools on the chart.

So what can we do? On the current version of Thinkorswim we can:

1. Add plot statements to plot data on the chart
2. Add chart labels to display data in the upper left corner of the chart
3. Add chart bubble to display data at specific time and price levels of the chart
4. Add vertical lines to display data at specific times on the chart

That's all of it. We have only those four tools to work with when writing custom chart studies on the current version of Thinkorswim.

If you want to plot a flat horizontal line on a chart, the only option we have available is the following:

plot lineOne = 100;

You can change the color and style of the line through the Edit Studies window. But there are no properties which allow you to add a label to that line, or extend the line to the right or left.