Let me as precise as possible. $u$ is an $r-1$-form such that $du=\varphi$. In particular, $du$ is of pure bidegree $(p,q)$. We have decomposed $u=\sum_{i=0}^{r-1}u^{i,r-1-i}$, where $u^{i,r-1-i}$ is the $(i,r-1-i)$ component of $u$. Then, we calculate $\varphi=du=\partial u+\overline{\partial}u=\sum_{i=0}^{r-1}\partial u^{i,r-1-i}+\sum_{i=0}^{r-1}\overline{\partial} u^{i,r-1-i}$. Now, $\partial u^{i,r-1-i}$ is an $(i+1,r-1-i)$-form and $\overline{\partial}u^{i,r-1-i}$ is an $(i,r-i)$-form. Thus, the $(r,s)$-part of $du$ is given by $\partial u^{r-1,s}+\overline{\partial}u^{r,s-1}$. Since …