FreeOffice: The command Remove duplicate rows is not included in SoftMaker FreeOffice.
To delete all duplicate rows within a certain range of rows, select the range from which you want to remove these rows.
Then choose 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 the corresponding contents in another row). It then deletes these duplicate rows.
Note
Normally, you select a range of complete rows before using this command. However, you can also select a cell range that doesn't consist of complete rows. PlanMaker will then ask you if you want it to delete the corresponding rows completely:
▪If your answer is Yes, all corresponding rows will be deleted completely.
▪If your answer is No, only cells within the selection will be deleted. The cells to the left and right of the selection will remain unchanged.