Import Data from file in MASS transaction

Dear Experts, can you please guide me on how to use "Import Data from File" option for MASS changes in PO. I need to set the flag "Service Based Invoice Verification" for the Service POs for which SES is not yet created.

I tried to set the flag using the field "Service-Based Invoice Verification" (LEBRE) in MASS t-code, but getting no values found message. Please help me with steps to use "Import Data from File" option in MASS t-code.