I would like to add two specific goal conversion completion numbers from Google analytics into one scorecard block in Google Data Studio. How can I do that?
You should be able to do that with a calculated field.
I'm assuming you already have your data source(s) linked to the DS report.
In the Menu Bar, click Resource > Manage added Data Sources
In the Data Source table, click Edit for the relevant Data Source
Once you are on the page with all the listed metrics, dimensions etc, at the upper right click the blue + Add a Field link In the field name area, give it an easily recognizable name and then start typing the goal in the formula box then select from list to complete it, add a + and then add the 2nd goal the same way.
Hit Save at the lower right. When you go back to your report, you should be able to add it as a scorecard
Really quick video walk thru of calculated fields by Google here: