Just traverse the node from root to left recursively until left is NULL. The node whose left is NULL is the node with minimum value.
Read full article from Find the node with minimum value in a Binary Search Tree | GeeksforGeeks
int
minValue(
struct
node* node) {
struct
node* current = node;
/* loop down to find the leftmost leaf */
while
(current->left != NULL) {
current = current->left;
}
return
(current->data);
}