Depends what you need

Diabetics are often deficient in any number of things. A dietitian can advise

But if you are asking what supplements will "treat" diabetes, then the answer is none.

Type 2 is a metabolic disorder and when "I" take chromium it takes my average sugar numbers down a little. But when a dozen other Type 2's take it nothing happens

Why?

Because "I" am chromium deficient and "they" are not

If you want to try a few and see if they do anything or nothing for you, here is a partial list of supplements that help "some diabetics, some time" - but they aren't meds so don't expect significant changes

Aegle Marmelos (Wood Apple)
Coriandrum Sativum (Coriander)
Syzygium Cumini (Black plum)
Murraya Koenigii (Curry tree)
Gymnema Sylvestre (Retz.)
Phyllanthus Emblica (Indian Gooseberry)
Momordica Charantia (Bitter melon)
Ocimum Tenuiflorum (Holy basil)
Coccinia Grandis (Ivy Gourd)
Zingiber Officinale Roscoe (Ginger)
Allium Sativum (Garlic)
Cinnamomum Verum (Cinnamon tree)

All may help a little, all may do nothing for you