Hello,
I'm afraid that without the current details ; we won't be able to give you any useful indication or guidance.
What "customization" ? What "button" ? What is the purpose or the meaning of your override ?
If we can't understand what you're trying to do, we can't point you the right file to modify.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.