How do I report escrow holdback for ISOs sale?

How do I report escrow holdback for ISOs sale? - Cost Basis unknown

Hello,

How should I report escrow holdback for ISOs sale?
I have received a separate 1099-B for escrow holdback amount, with just the proceeds and date disposed on the form. There is no cost basis, non-covered security box is checked and it says applicable checkbox for form 8949 is X.
I am unable to enter this 1099-B as per usual since Turbotax requires the number of shares sold and cost basis which is not applicable in this case?

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