Regarding query optimisation (select for update)

We are facing issues with slow running query 

   SELECT betid, versionid, betdata, processed, messagetime, createdat, updatedat FROM praermabetdata where processed = 'false' ORDER BY betid, versionid LIMIT 200 OFFSET 0 FOR UPDATE;  

                                                         QUERY PLAN
--------------------------------------------------------------------------------------------------------------------------------
 Limit  (cost=0.28..1.89 rows=1 width=78)
   ->  LockRows  (cost=0.28..1.89 rows=1 width=78)
         ->  Index Scan using idx_praermabetdata_processed_betid_versionid on praermabetdata  (cost=0.28..1.88 rows=1 width=78)
               Index Cond: (processed = false)

Do we have any alternative way to improve the performance?

Sometimes processed column use true as well as false 

Regards,

Durga Mahesh