12c: How to force oracle to use a different plan

Hi,

We have a sql which was running under a minute until friday.  From today morning, it is taking more than an hour to complete.   when , I checked the plan,

select  distinct SQL_ID,PLAN_HASH_VALUE from DBA_HIST_SQL_PLAN where SQL_ID='35v2mpxcqha0f';

35v2mpxcqha0f    1398877429

35v2mpxcqha0f    3144203662

it was using plan 1398877429 until friday which runs in less than a minute.   Today morning , it is using plan 3144203662.   How do I force oracle to revert back to old plan?

Thanks

Ram