A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
As Amit explained, the Freeze Panes button & the Unfreeze Panes button are one in the same. Yours currently reads as Unfreeze Panes because Freeze Panes already is applied.
In order to apply the Freeze elsewhere you first need to turn the current Freeze off by selecting Unfreeze Panes [the labeling of the button will change to Freeze Panes], select the appropriate cell then turn Freeze Panes on again.