There’s no standard spoon-for-spoon conversion. Tender Quick can cure beef, but substituting it for the tablespoon of pink salt and reducing the kosher salt requires a recipe developed for Tender Quick.

If “pink salt” means Cure #1, it contains 6.25% sodium nitrite. Tender Quick contains salt, sugar, sodium nitrite, and sodium nitrate, with different proportions and directions for use. Matching the saltiness won’t tell you whether you have the correct cure dose. See [Oregon State Extension](https://extension.oregonstate.edu/sites/extd8/files/catalog/auto/PNW784.pdf) and [Morton’s product guidance](https://www.mortonsalt.com/home-product/morton-tender-quick/).

[Morton’s deli-style corned beef recipe](https://www.mortonsalt.com/resources/meat-curing-deli-style-corned-beef/) uses 5 tablespoons of Tender Quick for a 4 to 6 lb brisket, with no additional kosher salt. You apply it as a dry rub with sugar and spices, then cure the brisket in the refrigerator for five days per inch of thickness. Those amounts apply to that dry-curing method and can’t be used as a conversion for your original brine.

To assess your recipe, I’d need the meat weight, water quantity (if any), curing time, and ideally a link to the recipe. The two salt quantities alone don’t provide enough information to calculate a reliable substitution.