If you want to have it match as close as possible, I would suggest a sand back on the underside first. This would give you a better idea where you stand and to select the satin you may want to use.
If you decide to sand back, make sure you sand with the grain otherwise it will show up when the stain is applied. Once you finish sanding, wipe down with methylated spirits to remove all sanding dust. At this point all sanding marks left will show up. Re-sand if needed and let dry. Do not us water. - r23on
Keep in mind that you might be able to stain light coloured timber to match a darker coloured timber but you won’t be able to lighten a darker tone. If a surface has a tint already you might be able to sand back the effect to expose the raw unfinished timber, but obviously there is a certain risk associated with that. I'd recommend you try on the underside first as a test in such cases. - MitchellMc
If it takes too much to sand down you may have to use Intergrain Timber Reviver. To test the results of staining and varnishing turn the top upside down and apply on a small tiny portion of the bottom of the top to see the possible results. Once you find something you like you can commit to staining the top portion. Let it dry indoors away from the sun. Once the stain/varnish has dried off then you may bring outdoors. Lightly sand and re apply once a year for longevity and protection. Apply extra on feet to protect against water soak in rainy season. - redracer01