Right click on the red arrow and select true.
The decision box always evaluates to a true and a false condition. Make sure that the true condition continues to a flow where your final outcome/result is defined so in this case you just have to right click on the arrow between the decision box and your activity box and select true.
While at the bottom just right click on the arrow and select false condition followed by an end activity or merge flow or another decision box based on your microflow design.
Hope this helps. Please mark the answer as accepted if this resolves your issue and has helped you to understand better :)