Substitute For Cream of Tartar
Cream of Tartar is potassium bitartrate in the form of powder. It is acidic, and is used in cooking mainly to stabilise meringue.

Tartare sauce is a mayonnaise-based sauce made using cornichons, capers, and tarragon or dill. It is usually served with seafood.

The two items are completely different and cannot be substituted one for the other.