How to append a new entry in custom table doctype during update customer API

Hi Team,
I have made a custom table doctype called Customer identification and have assigned it to Customer Doctype. Custom doctype consists of following field
Proof type: POA/POI
ID Type : PAN / Adhar card
ID No: xxxxxxxxxx
During customer creation i passed one entry say for eg POA : PAN : xxxxxxxx.

Now my requiremt is to update the customer and add a new row entry
Proof Type: POI
ID Type : Adhar card
ID no : yyyyyyyyyy

But when im trying to update the customer using Put call via postman, in body i am passing the new details. But on execution the old entry which was maintained during creation is getting overwritten.
Is there any way to maintain multiple entries, as my reuqirment is to maintain POA and POI both agaisnt the customer.