Too much:

Strong herbs such dill, thyme oregano etc - tie 3x as much parsley as the herb used into a muslin or herb bag and simmer in your soup for 15 minutes then remove and discard. Also works in sauces

Onions or Leek - add butter or olive oil and let simmer

Ginger - add butter, cream or dilute the taste with extra stock

Tomato - add sugar and a little basil or oregano

Vinegar - add sugar

Salt - potatoes don't work, add some sugar and lemon juice

Pepper - if it's unmixed, place a piece of bread over the top, it will suck it up. If it's stirred in, add lemon juice and sugar

Too :

Sweet - add balsamic vinegar and salt

Spicy - add cream of tartar, half to 1tsp per litre of stock

Sour - add sugar and salt

Thick - add boiling water or stock & adjust the seasonings. If it's a cream soup add milk

Thin - add instant potato flakes and bring to the boil or use some cornflour mixed with a little water instead. You can also puree a few ladles and add it back in

I hope these are helpful, they are all tried and tested!