You can do it yourself. HOWEVER, dogs can get their anals impacted, and at that point you will need to see a vet.
here's how to express normal glands. You will need exam gloves and lube. KY or vaseline is okay. Have some baby wipes or paper towel and mild soap available. I like to give my dog a full rear end shampoo after.
If you are not sure how your dog will react you will need a qualified holder and possiblity a muzzle. Keep in mind if your dog is impacted it can be painful. 'Fussy' dogs may cry out or even bite even if its not actually hurting them.
The glands are located at 8 and 4 o clock, one on each side. You want to be outside or in a bathtub for this. Put your gloves on and a bit of lube on your index finger. Use your right hand for the dogs left side and vice versa. Insert your index finger into the dogzs anus about an inch (for average size dog). You should feel a small (grape)(or sometimes it can be very large (walnut) with very full or impacted dogs) bulge. Using your thumb on the outside of the dog, you can squeeze the gland with moderate pressure, kinda like you were trying to pop a grape between both fingers. You might have to try a couple spots before you are able to release any fluid or paste. If you can't feel a bulge it means that gland is emptied at this time.
You shouldn't have to apply excessive pressure to release the glands..take your dog to the vet if you can't easily do it. picky glands can rupture if they are impacted too long, and they also are prone to infection; neither you want to deal with.
This is the way your vet office expresses glands. At groomers (at least in CA) they are not allowed to insert their finger because its considered medical if they do. I don't know how to do it this way...maybe someone else here does. I do know that the groomer way is almost impossible to express if the dog is on their way to being impacted.
Some dogs will need their glands emptied by a person on a regular basis. Signs they need it done is scooting (but keep in mind scooting is often a symptom of other problems, like worms) and licking the area. I do one of my dogs monthly myself otherwise she will once and awhile express in the house and I hate the smell! LOL
let me know if you have any questions.