Do not self attach cap. You need to clean the tooth and cap before attaching. You can't clean it thoroughly at home. It should not get contaminated with saliva... You can't stop it at home. Glues are not supposed in human body. You may accidentally swallow such illfitting cap. Do not experiment with yourself at home. Visit dentist.

Please do not attach it by yourself. You need to visit the dental clinic to get the cap fixed as it requires restorative material to fix the cap on the tooth. Doing it yourself will also cause you long term side effects  

You have visit your dentist for fixation

Please get it done in a clinic. Fixing it by yourself may lead to biting problem and interferences. Above all the glue type or gum you are asking for might create serious health hazards as the material might not be biocompatible. The biocompatible materials that a dentist uses are well reasearched and hence highly expensive. If cost is a factor for you, buying the cement itself will be much more expensive than getting it fixed in a clinic.