Why? There are a few reasons why your guitar's open tunings setup may need adjusting.
First, you don't want any harm to come to your baby ........ right?
Second, correct setup will make your guitar nicer to play. For most open tunings, the strings are tuned down (loosened) so the neck will relax a bit. Stuff like string buzz can be really annoying. A little is okay, especially if you like a very low action, but it should be minimal.
Third, if you intend to play any slide, the guitars open tunings setup needs to be set to specific tolerances. Especially so if you want to include some slide in your fingerstyle pieces.
So what to do? If you are unsure at all about making adjustments to your guitar, it's better not to take chances. Find a good repair person. It's wise to ask around. Remember to be specific with your questions. Some technicians are good with certain guitar work, and not so good with others. Some are wonderful with setups. Some aren't.
I don't know about you, but when my sweetie goes to the repair shop, I want her treated like family ........ I hope my wife's not reading this! Ahh, she probably knows.
If you already do setups or other work on your guitar, or you've decided to give it a try, here are some points to keep in mind. (Skip this if it's something you're familiar with already.)
SAFETY FIRST! What? We're not using a table saw or joining a gun club. True, but although it won't likely be fatal, if you get smacked in the eye with a breaking string you may lose it .... the eye! So especially when you raise the pitch (tighten the string) but even when you lower it, turn the instrument's face away from you.
Personally, I could count the number of strings I've broken almost on the fingers of one hand .... and that's after decades of tuning back and forth from standard to open and vice versa. And I've never broken a string when lowering. However, I've read that others have. Don't take chances.
The necks of guitars do not all react the same way to the same adjustments. Consider this an understatement! I was performing one evening at a theatre, and had changed my acoustic to an Open A Baritone tuning just a couple of days before. Because it was tuned so low, I was sure that heavy strings would compensate, keeping the neck in the same playable position.
Yeah, right. My idea was correct. The neck did adjust itself perfectly to the optimum position. But not till just over a week after my performance! I still hear those strings buzzing.
On the other hand, you may not need an open tunings setup. If your steel string guitar is an older or vintage instrument, it may not have a truss rod in the neck for adjustment. That's not necessarily a problem. Most guitars will tolerate lowering the tuning a couple of frets. Some with a higher action might play better when lowered to an open tunings setup.
Truss rod access is usually just in front of the nut. There's a little plastic cover, usually with 3 small screws. The other spot to look is in the soundhole for a hexagonal recess. Newer truss rods are often adjustable from both places. You'll need either a nut driver, a special wrench or an Allen Key.
A NOTE OF CAUTION: Any adjustments with truss rods need to be gentle and minimal. It is very easy to ruin your guitar! It's also vitally important to make sure there is still adjustment left in the truss rod. It may have been maxed out or over-tightened before. Always, always loosen first. To remember which way to turn, it's "righty, tighty....lefty loosey."