What you are requesting is a totally manual process if in fact it works. First thing you need to check are the tables to see if they have the same structure. If they do, you can empty them and import the data from your 3.7.4. If the data is okay, you will be able to get into the admincp to rebuild all your tables and counters and possibly be good to go. The process is time consuming and tedious, not to mention expensive if you need to hire someone to do it for you but it depends on how valuable the data is that you want to revert. Frankly, I think you are far better off trying to fix whatever the problem is in 3.7.4 and make that your platform of choice, at least its close to a supported version. I am assuming that you made a type with 2.6.8 meaning 3.68. Anyway, good luck with it.