Well, the key thing is opening it. You need a long reach Torx-15 to get the 2 screws in the handle to open it (there are 4, 2 in the handle and 2 at the bottom.) There are instructions to open the case online, look for a youtube video...
Let it sit for about 4 days so the high voltage caps discharge in that time.
Once the case is open, disconnect the crt socket at the end of the tube. Many end up smacking it and breaking the CRT when removing a stuck cable harness and it suddenly releases free! disconnect the hard drive and floppy drive cables, slowly. Then disconnect them from the mother board - again, slowly.
Now the hard part, The Power/Video cable is hard to pull out at times. There is a latch on it that you have press will pulling it out. Do this slowly. This is where many people pull too hard and it suddenly releases and they smack the CRT, breaking it. Removing the CRT Socket from the tube will lessen this from happening but you can still hit the tube and break it. So use caution and take your time with it. With it removed, the Logic board should slide back and out from a set of groves in the frame.
Look for a battery in a covered box. The top of the box clips to the bottom at the front and back. It's easy to remove once you figure out how the clips are on. Sometimes it might not have a cover. In either case with the cover removed - pull that battery out! It's a 1/2 AA at 3.2 volts. You can get a replacement at most electronic shops or online. Its about $10. Do not replace the battery until after it get a recap first. But IT IS IMPORTANT that you remove the battery as soon as you can! Old batteries tend to explode and dump their corrosive chemicals onto the board and destroying it. Once the battery explodes and the damage done, the board is junk. This is why you need to do this immediately! As soon as you can!
Now the expensive part- GET THAT BOARD RECAPPED!
The capacitors on the SE/30 go bad and tend to rot the board in the same way an exploded battery would. But this damage is repairable, where an exploded battery damage is not. A few people here, including I, recommend member Uniserver's recapping service. He replaces the caps on the board for a low price and fixes other issues he finds, so you are getting a near 100% working board. He is highly recommended. PM him about how much to get it done - all parts and labour included.
Also ask about recapping the Video board and power supply.
The caps he uses are ceramic or tantalum caps, ensuring that the board will be functioning for another 20 or more years. I would not be surprised if it lives for another 100 years - LOL!