Since you are really only displaying the data, recreate your fields in customer_info as 3 global fields, then you can set the global customer id with a drop down value list comprised of all customer ids (you can hide the id itself and just show the name, but just the id will be entered into the global id field), and the other two with drop down and/or radio buttons. Put this on a new layout from new TOs still pointing to the original tables. Note if you want to display any of the data from the customer table on this new layout (and you probably will) create an additional TO of the customer table and relate the global customer id to the _kp-customer_id.
This is call portal filtering and I'm pretty sure you can find more erudite explanations by searching these forums, but this should get you started.
Define a new field to use for your drop down list so that selecting a customer here does not change the customer ID in the current record. As Bumper suggests, this can be a global field and that will work best in the following script:
Enter Find Mode 
Set Field [customer_info 3::_kp_customer_id ; Customer_info_3::gCustomerID]
This script, as written, will only work if gCustomerID is set to use global storage in field options. You'd place this new field on your layout, format it as a drop down or pop up and either put a button next to it or use a script trigger to perform the above script.