Need to update duplicate Zoho salesIQ client data into crm

Need to update duplicate Zoho salesIQ client data into crm

Hi,
my issue is that, if some one fills the pre chat form that data goes into the crm, and if some one renter the data into the pre chat form then that data also goes to crm excet of updating the previous client it will makes an other client.

is their any one who can help me on that.

Thank You!