It depends on what the underlying-glue is like...is it gone very tacky or begun to break -down?... usually the glue is still quite `sound`on the skin...just that the lace has lifted from it.....applying a little fresh glue on top of the existing glue will do the trick....if the glue has become `unstable` or kind of messy, you`ll have to remove it with a solvent or glue-melter which has been applied to a soft cloth ....this can be `fiddly`/ tricky as you can often end up with more of the system lifting than just that one area..... I think you`re using Ultrahold now [ your other thread-question said so] ...those acrylic glues can be `stringy`...best way to apply them is dip your applicator [coffee-stirrer or whatever] into the bottle, then lift it out....allow the excess glue to run off /drip back into the bottle naturally...don`t `tip`the applicator off the rim of the jar to remove it or you`ll end up with these long strings of glue hanging off the applicator...allow all the excess to run off /drip back into the bottle itself and then you can apply it to the required spot under your lace. Chances are it`s just that the lace has come free of the glue rather than the glue actually breaking-down. A light/fresh layer of glue can usually do the trick without using alcohols etc..... I did a reply on your other thread in which I suggest that you may need an extra layer of glue at the initial bonding, to avoid lace coming free like this....suggest it to your stylist and see if that helps next time.