FreeOffice: The command Remove empty rows is not included in SoftMaker FreeOffice.
To delete all empty rows in a certain range of rows, select the range from which you want to remove empty rows.
Then choose the ribbon command Data | group Edit | 
Remove empty rows.
PlanMaker scans this range for rows that are completely empty, (i.e. where none of its cells is filled with a value). It then deletes all matching 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.