Hi. Thank You for the question. I hope this will be helpful for other people using HQ Plants as well.
Since FP7 HQ plants installer can't find Forest Pack Installation. Not sure why it searches, but it does not find with following error:

Workaround is extracting installer files manually (we recommend
7zip file archiver):

Once extracted You get these files:

We only need lib folder. Delete the other 2.
Now Open Forest Pack Library Browser Preferences window:

And add location where extracted lib folder is:

Double Click or F2 to rename added location:

Further steps are the same as usual, when loading the plant first time You will have to point to an actual folder where the library is located:

Hope this helps.