Hoping to do this with one product as opposed to Staining then having to Varnish.
then prepare to be disappointed
if you use a tinted varnish or similar, the pale bits will still be paler than the dark bits.
you need to sand it back. It looks pretty flat so light, fine sanding may be enough. Look at the underside and the edges to see if the timber is solid or veneered. Veneer is very thin and will take very little sanding.
Depending on age and quality, it might be French Polished or varnished. Might be oiled though I don't think so.
The damage might be water damage. If you can sand off the discoloured surface you won't need to colour it; otherwise you must strip off all the finish and use a spirit-based wood dye (not stain).
Wilko do a surprisingly good range (probably made and labelled for them by Blackfriar or some other major maker). Don't use Colron "refined" range, it's rubbish.
start with a dye a little lighter than you think you need, you can darken it if not right.
you can mix dyes of the same brand in an eggcup. They are just variations of brown, yellow, red and black.
you need hardly any dye
use can use a fine paintbrush and a darker dye to simulate graining if it will hide the damage.
If you use a varnish, a matt or satin will look less garish than gloss.