FreeOffice: The command Remove duplicate rows is not included in SoftMaker FreeOffice.
To delete all duplicate rows in a certain range of rows, select the range from which you want to remove these rows.
Then select the ribbon command Data | group Edit | 
Remove empty rows 
| Remove duplicate rows.
PlanMaker scans this range for rows that are completely identical, (i.e. where the contents of all cells in one row are identical to another row). It then deletes these duplicate rows.
Note
Normally, you use this command with a range of entire rows selected. However, you can also select a cell range that doesn't consist of entire rows. In that case, PlanMaker will first ask you if you want it to delete matching rows entirely:
▪If your answer is Yes, the entire row will be deleted for all matching rows.
▪If your answer is No, only cells inside the selection will be deleted. The cells left and right of the selection are not affected.