Hmmm this might be a bit tricky
I do my dog's glands whilst they are in the bath, before I shampoo, that way any nastiness can be washed away immediately.
OK, if the dog is in the bath, head facing right, hold the tail in the left hand & with the right hand put finger & thumb either side of the anus.
Apply pressure towards the head & gently squeeze at the same time, if the glands are full, you should be able to feel this, it's like two marbles.
Doing this should empty them, sometimes if you get no joy, they may not need doing, or you may have to have another go because you weren't doing it correctly.
You will find, that you get better with practice
One tip is that you may need a willing partner to hold the dogs head, as some really dislike it
Maybe someone else can put it better than I can, hope I've helped a little.