ORA-03297 on Oracle Tablespace alter
You have segments allocated across the tablespace with "gaps" of free space. 
In order to reclaim it you should first reorg the tablespace. 
See: reclaiming unused space
https://oracle-base.com/articles/misc/reclaiming-unused-space
It's a rather long process for such a large file.... 
Btw, if you have EM installed it's just a couple of mouse clicks 

Regards 
Jony