What are the explicit expressions for the creation and annihilation operators $\hat{a_\vec p}$ and $\hat{a}^{\dagger}_\vec p$ for bosons? I can't find them anywhere, as every source seems to introduce them when quantizing the fields
$$\phi(\vec x) = \int \frac{d³p}{(2\pi)³} \frac{1}{\sqrt{2\omega_{\vec p}}}  \left( \hat{a_\vec p} e^{i\vec p \cdot \vec x} + \hat{a}^{\dagger}_\vec p  e^{-i\vec p \cdot \vec x}\right)  $$
$$\pi(\vec x) = \int \frac{d³p}{(2\pi)³} (-i) \sqrt{\frac{\omega_{\vec p}}{2}}  \left( \hat{a_\vec p} e^{i\vec p \cdot \vec x} - \hat{a}^{\dagger}_\vec p  e^{-i\vec p \cdot \vec x}\right)  $$

Without giving an explicit expression for them.
I would like to know, because e.g. calculating the Hamiltonian for the Klein-Gordon field requires me to know what effect switching the sign of the momentum has, i.e. what  $\hat{a}_{-\vec{p}}$ and $\hat{a}^\dagger_{-\vec{p}}$ are.