It depends what you've got to clean/remove glue with? You might need to let the lace & hair sit in a dish of the stuff to get it out of the hair, when the piece is off.
Once the glue is softened, you can then do the mirror slide.

This is how I attach mine.
Scalp dry, piece dry. Put the piece in its right position on my head.
Fold back the front so I can see the lace side (Still holding it in the right position on my head.)
I use a make up pencil and put 2 dots on either side of my scalp, approx 2-3 inches back from the hairline. I fold the lace back to where it meets the dots and mark the underneath of the lace at those same 2 points.
So I can remove the piece and put it back again and as long as the dots all match up, it will always go back in the right position. (I hope that makes sense?)

With the piece in position, I use the teeth of a comb and press them in to my scalp all along where the lace front hairline is & ends.
So when I remove the piece to apply the glue, the dents in my scalp show me exactly where to apply the glue up to along the hairline.

I put on 2 layers of Oil Resistant White Glue.

When they're dry, I put the piece back on, matching the dots and the edge of the glue exactly matches the edge of the lace front.
I use the teeth of the comb and go along the edge of the hairline and press the lace in to the glue.

I do my attachments at night so the glue hardens whilst I sleep.
By morning I can spritz it with water and style it and it doesn't affect the attachment.

I also cut my lace back right to where the hairline is. Some people leave a bit of extra lace (1-2 millimetres)

As I say, I hope I've explained it clearly.