Click the Existing Activities button, then select External Learning Tools.
Click the External Learning Tool title from the list (note there are multiple pages of tools available).
Depending on the product you chose, you might need to do an additional step to open the link in a new window. If this is the case, do the following steps:
Click the context menu next to the topic title, then select Edit Properties In-place.
Check the box for Open as External Resource to open the link in a new tab.