If the string read has a certain decimal value, then reading the next digit changes that value  : multiply by $10$ and add that digit. The DFA keeps track of that value modulo $43$. Thus, for $q\in \{0,1,\dots,42\}$ and $a\in \{0,1,\dots,9\}$, $\delta(q,a) = 10\cdot w + a \bmod 43$.

If the string read has a certain decimal value, then reading the next digit changes that value: multiply by $10$ and add that digit. The DFA keeps track of that value modulo $43$. Thus, for $q\in \{0,1,\dots,42\}$ and $a\in \{0,1,\dots,9\}$ you do

$\qquad \delta(q,a) = (10\cdot q + a) \bmod 43$.

Note that the DFA does not actually perform the computation; the transition is hard-coded.