To restore to its original condition, suggest to re-stain it. Here are brief steps:
1. sand down to bare wood and fix scratch if any
2. apply new stain (2 times)
3. apply 2~3 clear coats
You can google the details for each step. It is always easier saying it than doing it. The selection of stain might be tricky, same stain can show different color on different wood. Try small sample first, normally less than a dollar. Be aware of safety procedure.