If you are referring to checking the VSE 8.5 package into ePO, try using the Previous branch instead of the Current branch in the repository (this is just a guess, haven't tried it myself - I thought both versions could be in the Current branch). Then when you deploy 8.5, have it deploy from the Previous branch.
If you are referring to a system that has 8.7 installed, and you want 8.5 installed instead, you will have to create a VSE 8.7 deployment task for that system and set the action to "Remove". After it is removed, delete that task and create a VSE 8.5 deployment task for that system. You may want to disable the "Run at every policy enforcement" option and/or delete the task once you are sure 8.5 installed properly.