Download and install the newest version of OSATE from https://osate-build.sei.cmu.edu/download/osate/stable/ The current version (November 2019) is 2.6.0.
The BLESS plugin(s) can be installed into OSATE 2.6.0 as an update site by Help -> Install New Software.
Click the Add button. The Add Repository window opens.
Name: BLESS Location: http://multitude.net/update Click Add button.
Check the box beside “BLESS”. Click Next. Read then accept the licenses. Finish.
OSATE will ask whether to restart. Do so.