Lightly sand off sheen and wash down with TSP. Use a gel stain that does not have finish in it. Coat with oil based varnish or lacquer.
You can stain over stain using gel stain with minimal prep. You can go darker but not lighter. Minwax has instructions.
Sand, clean with tsp or vinegar and water, then stain. It is much easier to go from light to dark stain than the other way around. If you can’t get to the oak stain in the corners and seams with a sander, fold a sheet in half and use your hands to push the sandpaper into or next to the crevices. Please take photos and post this on Hometalk.com. There is a template which will take you through the process. Jewell
First you must remove any top coat for the stain to take, you can sand, use 000-0000 steel wool to remove, wipe with a paint stripper to be sure its all gone. Then use a wood conditioner to get a smooth even finish.