After synchronizing your index, you can re-collect statistics on a single index to update the cost estimates.
If your base table has been re-analyzed before the synchronization, it is sufficient to analyze the index after the synchronization without re-analyzing the entire table.
To do so, enter any of the following statements:
ANALYZE INDEX <index_name> COMPUTE STATISTICS;
or
ANALYZE INDEX <index_name> ESTIMATE STATISTICS SAMPLE 50 PERCENT;