How do i Reduce the basis of my stock by distributions?

It depends on the type of distribution. If you receive a tax free distribution (usually, a “return of capital”), you do reduce your cost basis for the amount of the distribution. You show nothing about the distribution, on your tax return. You only adjust the cost basis, on your own records, for when the stock is sold in the future.

Ordinary stock dividends are taxed as income and do not affect your basis.

For distributions of additional shares, your original cost basis remains fixed and is just spread over more shares. For example; if you originally bought 100 shares for $1000, your cost basis was $10/share.  If you receive a distribution of 10 additional shares, your  cost basis in the 110 shares is still $1000, but is now $9.09/share (1000 / 110)