These sealants must be cured with heat. Apply 120-140C air from the heat-gun (soldering station or whatever). After it's been cured, excessive residue to be removed mechanically so that it won't introduce any obstacles on the LOCA glue path, flowing down LCD sides. Nothing to say the sealant must not overhang LCD surface. The strong property of these sealants is that those are easy to remove from protected surface. But only if it's properly cured! ,) UPD I bought three of these: the Clear,the White and the Blue. Clear & White eppear to get cured by both heat and UV lamp; the Blue only got cured by heat.
Not only the problem is to remove the (cracked) glass, which is achievable rather simple with the help of some sort of unglueing treatments (like the GooGone and etc.), but to rebond the new glass lens with the LCD-digitizer assembly (yes, the LCD and digitizer in iPhone 5 are glued together and this assembly is then glued with the display glass lens). There is a special (industrial) optically clear adhesive used, which also eliminates the air bubbles after treatment. Unfortunately, this glue is unavailable across the USA and Europe. Likely it is only available in China and maybe some other countries, where the manufacturers plants reside. UPDATE! The afore mentioned glue is called LOCA (Liquid Optically Clear Adhesive), it's made by Loctite and is currently widely available from ebay or aliexpress.